Limp Mode and DTC 452

I have a 94 with the 5.8L. 157k. I need some help to get the beast reliable for me and my son to do some off-roading.

It keeps going into limp mode. I have already replaced TPS, MLPS and VSS. Keep getting DTC 452. Also checked for shorts in the common locations but none were found.

Bronco will run fine sometimes but then when I apply the brakes the battery voltage will drop on the dash gauge and it will start limping. When this happens the voltage will drop significantly if I sit with my foot on the brake. I can watch the voltage keep dropping until it almost stalls out. Also, if I turn on my headlights the voltage drops and it will go into limp mode sooner. The problem seems to take longer to occur during the day since I am not using the headlights.

Could my alternator be bad? And if so, could that cause the limp mode and code 452?

Well you can take the alternator to a parts store and they can check its good, most times for free, or you can do it the way I was taught ( which I've heard bad things about but I've never had ne thin happen) you can pull the positive battery cable off while the truck is running and if it dies then the alternator is bad.

yo dssumners,

WELCOME!

As 90 advised, have a fully charged batty abd scan for Codes again.

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

Do Key On Engine Off (KOEO) portion first.

Look Codes up in my broncolinks.com site using the new Search function.

And Post em here according to:

KOEO

&

KOER

Is your 4WABS functioning normally? Is the PSOM (speedometer) working properly? If so to both that indicates that the signal is good up to that point

The programmable speedometer/odometer (PSOM) module receives input from the rear brake anti-lock sensor (ABS) (also referred to by many including Ford as the Vehicle Speed Sensor (VSS)) which is mounted on the 8.8 diff. housing via some connectors and through the 4WABS Module).

The PSOM processes this input signal information & relays it to the powertrain control module (PCM) and the speed control module. This signal tells the powertrain control module the vehicle speed in miles per hour (mph). Used as an input in determining shift scheduling & electronic pressure control.

Path from; Rear Anti-Lock Brake System (RABS) Sensor (also called Vehicle Speed Sensor (VSS) & Differential Speed Sensor (DSS); through Connectors & 4WABS Control Module, etc to PSOM, PCM & E4OD & to Cruise (Speed Control)

452 Erratic Harsh Shift; PSOM Operates Correctly; "...Continuous Memory DTC 29 indicates that during the last 80 warm-up cycles, the PCM detected an error in the PSOM output signal. DTC 452 indicates the PCM detected an error in the PSOM output signal during the last 40 warm-up cycles. his procedure EXACTLY, from the Ford TSP/PCED.

Possible Causes:

-- Damaged Rear Anti-Lock Brake System (RABS).

-- Damaged PSOM.

-- Damaged harness circuits.

-- Damaged PCM.

Where breakout box is mentioned , go to the EEC pin instead; for instance -

"Measure resistance between Test Pin 3 and Test Pin 6 at the breakout box"

go to this Connector Pin Depiction Pic by Ryan M (Fireguy50)



& Ryan's LEGEND so you know what you are testing

Pierce the wires with a straight pin (I use wife's sewing str pins w/plasctic ball @ end); backprobing is diff due to silicaone gasket.

Pin 3 is VSS (+)

Pin 6 is VSS (-)

l Key off.

l Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.

l Install breakout box, leave PCM disconnected.

l Measure resistance between Test Pin 3 and Test Pin 6 at the breakout box.

l Is resistance between 21,000 and 55,000 ohms?

Yes

GO to «DS4».

No

GO to «DS2».

DS2 CHECK CONTINUITY OF THE HARNESS CIRCUITS

l Key off.

l Breakout box installed, PCM disconnected.

l Disconnect PSOM.

l Measure resistance between Test Pin 3 at the breakout box and PSOM(+) circuit at the PSOM vehicle harness connector.

l Measure resistance between Test Pin 6 at the breakout box and PSOM(-) circuit at the PSOM vehicle harness connector.

l Is each resistance less than 5.0 ohms?

Yes

GO to «DS3».

No

SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN «Quick Test».

Quote:

DS3 CHECK HARNESS CIRCUITS FOR SHORTS TO POWER AND GROUND

l Key off.

l Breakout box installed, PCM disconnected.

l PSOM disconnected.

l Measure resistance between Test Pin 3 and Test Pins 6, 37 and 40 at the breakout box.

l Is each resistance greater than 10,000 ohms?

Yes

GO to «DS4».

No

SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN «Quick Test».

Quote:

DS4 CHECK RABS SENSOR RESISTANCE

l Key off.

l RABS disconnected.

l Measure the resistance of the RABS.

l Is resistance between 1300 and 1550 ohms?

Yes

GO to «DS5».

No

REPLACE the RABS. REMOVE breakout box. RECONNECT all components. RERUN «Quick Test».

Quote:

DS5 CHECK PSOM OUTPUT VOLTAGE

WARNING:

THIS TEST STEP REQUIRES ANOTHER PERSON TO ACCOMPANY THE DRIVER TO MAKE MEASUREMENTS AND RECORD DATA. ALL APPLICABLE SAFETY PROCEDURES AND TRAFFIC LAWS MUST BE FOLLOWED.

l Key off.

l Breakout box installed.

l Reconnect PCM to breakout box.

l Reconnect PSOM.

l DVOM on 20 volt AC scale.

l Warm engine to operating temperature.

l Measure AC voltage between Test Pin 3 and Test Pin 6 while gradually increasing vehicle speed to 50 mph.

l Is the maximum voltage received greater than 4.0 volts?

Yes

REPLACE PCM. REMOVE breakout box. RERUN «Quick Test».

No

REMOVE breakout box. RECONNECT components. REFER to the Instrument Cluster, Speed Control or Brake Group in the Service Manual for further diagnosis.

.."

Source: by SigEpBlue (Steve)

Limp Mode; "Fail Code" conditions or "Limp Mode" happens when the vehicle computer recognizes a problem in it's logic. When an expected signal value from a sensor is sent to the computer and is not within the computer's programmed specifications, "secondary" programs are activated by the computer to strive to protect the transmission from damage the improper sensor signal might cause to occur.

In other words, the computer is always expecting certain signal values from certain sensors i.e. the temperature sensor, the speed sensor, the throttle position sensor, etc. As long as these signals are what it would normally expect for the conditions and is normal based on all the other signals it is receiving from other sensors, it acts normally and accordingly.

If the computer, all of a sudden, receives some crazy signal from one of the sensors that is out of the normal range expected from this sensor, it will go to "emergency" or "secondary" measures.

These emergency measures vary depending on the severity of the defective signal. All this is preprogrammed into the computer's logic by the manufacturer. The manufacturer has decided that as long as a certain parameter of a particular signal is sent from a sensor to the computer, all is well. The manufacturer decided that if this signal is higher than their highest parameter or lower than their lowest parameter, something is wrong with that sensor and the computer should make someone aware of the situation and take action to try to "save" the vehicle systems or powertrain.

Perhaps the computer will simply cause the "check engine" light to come on. The signal variation wasn't severe or critical to cause any mechanical failures but the vehicle's operator is made aware that he or she should have the vehicle checked out electronically to see if a minor sensor has broken down or is starting to send the odd irratic signal. This type of condition is commonly referred to as a "soft code". Normal functions are not affected but if the repair is not made, performance or fuel efficiencies might suffer. Perhaps the sensor only malfunctioned one time and all other times was fine. This might be an early warning of a sensor that is beginning to fail or has a loose connector or connection.

Other times the signal needed to perform operations normally is so far out of specification that the computer has no choice but to go into survival mode. With transmissions, the computer will cause the internal tranny fluid line pressure to default to high to protect clutches and bands. The transmission also turns off the shift solenoids to cause the unit to default to a single gear, usually second or third. All normal instructions to control line pressure are overridden so a hazardous "slipping condition" cannot occur easily. This theoretically is so that the vehicle's driver can get the damaged vehicle to the next town for repairs. This condition is commonly called "Limp Mode" for this reason. You limp to the next town in second or third gear only, at full line pressure so the tranny guts won't slip on your trip in.

By the way, interestingly and just as a side note, if the cable harness going to your transmission was ever to become detached, severed or damaged, your transmission would also go to "limp mode".

The vehicle's computer would immediately sense that it has lost contact with the transmission and would set the codes and send "limp mode" signals to the tranny. But because the harness is severed between the computer and the transmission, no computer signals will reach the transmission. These sent signals, however, would have had the identical affect on the transmission as what taking away supplied power to the shift and line pressure solenoids has as in the case of a transmission harness being detached or cut. Due to the engineered voltage strategies of the solenoids, the transmission simply defaults to a single gear and line pressure defaults to high, all in order to "limp" you home.

A Throttle Position Sensor that improperly sends a reading that it is wide open when in fact it is physically closed would be detected by the computer when it compared this reading with the vehicle speed sensor that perhaps is showing very slow vehicle speed. The signal, by itself can't be considered wrong but when put against all the other sensor signals of the system might cause a computer concern. The computer, at this point, unable to "trust" the collection of signals because together they are not making sense in it's logic, will simply go to limp mode in the transmission to protect it and make the operator aware that something is wrong with one of the sensors and a mechanic's attention is needed to correct the situation.

This Fail Code Condition will show up as a "code" reading on a mechanic's scanner. This code will be cross referenced to a table from the manufacturer and represent a problem with a particular sensor or a group of sensors or system. It gives the mechanic a better idea of where the problem has showed up and which systems or sensors are involved in the malfunction. The table of codes and what each one means, is commonly programmed right into the scanner tool that the mechanic uses for easy reference.

i.e. the scanner tool might tell the mechanic that the computer has thrown a code "35" which is the "transmission fluid temperature sensor" and might give the mechanic the recommended values this sensor should provide and what it in fact provided...

In your electronic transmission, many important functions are controlled by the computer. Shift timing, sequence, feel, line pressure are controlled. The information from the vehicle speed sensor affects fuel injection, fuel mixture, ABS, transmission operation, etc. Load information of your engine is commonly taken primarily from the TPS (throttle position sensor) or the MAP sensor (manifold absolute pressure). This controls transmission shifting and downshifting when stepping on the gas or climbing hills. A regular scanning of the computer for any set "hard" or "soft" codes is something routinely done by most good tuneup shops these days.

Source: by Greg O at autotransinc.com via webarchive.org http://web.archive.org/web/20050206072713/http://www.autotransinc.com/limp.htm

Thanks for the response. I will have to get to all the probing of the electrical stuff when I get a day off. So you do not think that a bad alternator could cause the condition? Just wondering because of the voltage drop when I run the headlights or put on the brakes. It will be fine for a while, but then it is like the voltage gets drained down then the limp mode starts.

Sorry if I sound ignorant, but I am new to trying to work on a vehicle myself. My wife calls it cheap, I call it thrifty.

dssumners said:

Thanks for the response. I will have to get to all the probing of the electrical stuff when I get a day off. So you do not think that a bad alternator could cause the condition? Just wondering because of the voltage drop when I run the headlights or put on the brakes. It will be fine for a while, but then it is like the voltage gets drained down then the limp mode starts.

Sorry if I sound ignorant, but I am new to trying to work on a vehicle myself. My wife calls it cheap, I call it thrifty.

Click to expand...

yo D,

Could be due to low voltage taht will affect TPS, VSS, etc.

Get the alt and batty checked out for free at local parts store.

Check alternator output, must be between 13.5 and 14.5 volts.

Voltage; "...a normal battery that is fully charged produces 12.6 volts, not just 12.0 V. (Remember, when measuring battery voltage, everything in the car should be off, or the battery should be disconnected. Voltage measurements are always "no load" measurements unless the battery is being tested for it's performance under load)..."

Thanks miesk5!!! The battery is new, but I will go get battery and alternator tested Friday. I will let you know what I find out.

Alright miesk5, here is what I got. Battery tested fine, 12.5 V. When I cranked the vehicle and turned on the headlights I was getting between 15.4 - 16.8 V. The reading was bouncing around all over the place.

Please give me some good news and tell me how to fix my problem.

Thanks.

After thinking about it some more, could my alternator be bad (specifically the voltage regulator)since the voltage is so high but then drops sometimes when I have my headlights on and press the brake. This drop may cause the code 452 since it is not sending enough voltage to the VSS. Just me thinking, but I defer to someone who knows a lot more about this stuff than me.

yo D,

That is high voltage output

engine at 1500 rpm with no electrical load. AC off, same for blower motor, lights, etc.

The voltage should be in the range of 14.1 to 14.7 volts.

Symptom Chart

Voltage Gauge Reads High

Damaged regulator. Most Likely

Charge indicator. Is Indicator Lamp On with Engine Running?

Alternator. See TSB below and check alt batty terminals and grounds.

Check this out, although 94 isn't listed;

[TSB-96-21-4/CHARGING-GENERATOR-DISCHARGE-LOOSE-OR-WEAK-CONTACT-AT-GENERATOR-HARNESS-CONNECTOR--WIRING-GENERATOR-HARNESS-CONNECTOR-DAMAGED-LOOSE-OR-WEAK-CONTACT.html"]Loose or Weak Contact at Generator Harness Connector TSB 96-21-4 for 86-93 Bronco & F Series, etc.

When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness, resulting in increased resistance. The increased resistance produces more heat. When the generator is replaced, the resistance produced by a damaged connector may damage the new generator and could result in a repeat repair, including installation of another generator. High resistance (caused by a damaged connector) will not go away until the damaged connector is replaced.

ACTION:

Visually inspect the harness-to-generator connector for damage (heat, corrosion, distortion and cracking) before installing a new generator. Install the Generator Wiring Harness Connector Kit (E5AZ-14305-AA) if the harness-to-generator connector is damaged.

The Generator Wiring Harness Connector Kit (E5AZ-14305-AA) contains the following:

•One (1) Red Wire Butt Connector

•Two (2) Yellow Wire Butt Connectors

•One (1) Wire Connector Assembly

•One (1) Instruction Sheet (I.S. 6849)

PART NUMBER PART NAME

E5AZ-14305-AA Generator Wiring Harness Connector Kit

The connector looks good. I checked everything again this morning. Battery is good but alternator was running 15.7V. I drove around for about 15 minutes with no problem. Then I stopped and turned on the air conditioner and the voltage gauge dropped. I checked at the battery and was only getting 12.7V. I am going to throw a new alternator on Monday and see if that works. I will let you know.

Thanks

Yo DS,

Can you take the Bronco to local partsd store that will test althernator (& entire charging system) for free?

This is what Ford would do;

Battery and Charging System, Service 1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual

DIAGNOSIS AND TESTING

same for 02;

Capacity Testing

To perform this test, use a high rate discharge tester, Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent, in conjunction with Rotunda 73 Digital Multimeter 105-R0051 or equivalent.

Turn the control **** on the ARBST to the OFF position.

Turn the multimeter selector switch to the DV volt position.

Connect ARBST and multimeter positive test leads to the positive battery post and both negative test leads to the negative battery post. The multimeter clips must contact the battery posts and not the ARBST tester clips. Unless this is done, the actual battery terminal voltage will not be indicated.

Turn the load control **** in a clockwise direction until the ammeter reads approximately half of the cold cranking amps of the battery.

With the ammeter reading the required load for 15 seconds, note the multimeter reading. Avoid leaving the high discharge load on the battery for periods longer than 15 seconds.

If the multimeter reading is 9.6 volts at 21°C (70°F) or more, the battery has a good output capacity and will readily accept a charge, if required.

If the voltage reading obtained during the capacity test is below 9.6 volts at 21°C (70°F), and the battery is fully charged, the battery is defective and must be replaced. If unsure about the battery's state of charge, charge the battery.

After the battery has been charged, repeat the capacity test. If the capacity test battery voltage is still less than 9.6 volts at 21°C (70°F), replace the battery. If the voltage is 9.6 or more at 21°C (70°F), the battery is satisfactory for service.

If the battery is found to be discharged only, check for a loose drive belt, loose electrical connection, charging system performance, and perform battery drain testing as described in this section.

Base Voltage Test

NOTE: Prior to running this test, turn the headlamp bulbs (13007) on for 10-15 seconds to remove any surface charge from the battery. Then, wait until the voltage stabilizes before performing the base voltage test.

With the ignition off and no electrical loads on, connect the negative (-) lead of Rotunda 73 Digital Multimeter 105-R0051, or equivalent, to the battery ground cable (14301) clamp.

Connect the positive (+) lead of the voltmeter to the battery to starter relay cable (14300) clamp.

Read and record the battery voltage shown on the voltmeter. This is called base voltage and will be used in later tests.

No-Load Test

Connect Rotunda 88 Digital Multimeter 105-R0053 or equivalent to monitor engine speed.

Connect the leads of Rotunda 73 Digital Multimeter 105-R0051 or equivalent across the battery terminals.

Read the voltage (base voltage).

Start the engine (6007).

Run the engine at 1500 rpm with no electrical load.

Read the voltage. The voltage should be in the range of 14.1 to 14.7 volts. If the voltage increase is less than 2.5 volts over the base voltage, perform the following Load Test. If there is no voltage increase or the voltage increase is greater than 2.5 volts, perform the Generator On-Vehicle Tests and Generator Bench Tests in the Diagnosis and Testing portion of this section.

Load Test

With the engine running, turn the air conditioner on, if equipped, the blower motor (18527) on high speed and the headlamps on high beam.

Increase the engine speed to approximately 2000 rpm. The voltage should increase a minimum of 0.5 volts above the base voltage. If the voltage does not increase as specified, refer to Generator On-Vehicle Tests and Generator Bench Tests in the Diagnosis and Testing portion of this section.

If the voltage increased as specified, the charging system is operating normally. Proceed to the following battery tests.

Field Circuit Drain

Alternate Test Method

Use Rotunda Power Sensor Plus Electronic Battery Test 162-00002. Follow the manufacturer's defined test procedure.

Drain Testing

Check for current drains on the battery in excess of 50 mA with all the electrical accessories off and the vehicle at rest. Current drains can be tested with the following procedure.

WARNING: DO NOT ATTEMPT THIS TEST ON A LEAD-ACID BATTERY THAT HAS RECENTLY BEEN RECHARGED.

CAUTION: Do not crank the engine or operate accessories that draw more than 10A. You could blow the fuse in the meter.

NOTE: Many computers draw 10 mA or more continuously.

NOTE: Use Rotunda 88 Multimeter 105-R0053 or equivalent between the battery positive or negative post and its respective cable.

NOTE: Steps 1-5 correspond to the numbers in the following illustration.

Insert the test leads in the input terminals shown.

Turn switch to mA/A DC.

Disconnect battery terminal and touch probes as shown.

Isolate circuit causing current drain by pulling out one fuse after another while reading the display.

Current reading will drop when the fuse on the bad circuit is pulled.

Reinstall fuse and test components (including connectors) of that circuit to find defective component(s).

Typically, a drain of approximately one amp can be attributed to an engine compartment lamp, glove compartment lamp, or luggage compartment lamp staying on continually. Other component failures or wiring shorts may be located by selectively pulling fuses or disconnecting fuse links to pinpoint the location of the current drain. When the current drain is found, the test lamp will go out or the meter reading will fall to an acceptable level. If the short is still not located, after checking all the fuses and fuse links, the drain may be due to the generator.

Test Conclusion

The current reading (current drain) should be less than 0.05 amps. If it exceeds 0.05 amps it indicates a constant current drain which could cause a discharged battery. Possible sources of current drain are vehicle lamps (underhood, glove compartment, luggage compartment, etc.) that do not shut off properly.

If the drain is not caused by a vehicle lamp, remove the fuses from the interior fuse junction panel, one at a time, until the cause of the drain is located. If drain is still undetermined, remove fuses one at a time at the main fuse junction panel to find the problem circuit.

Electronic Drains Which Shut Off When the Battery Cable Is Disconnected

Repeat Steps 1 through 6 of the voltmeter drain testing.

Without starting engine, turn ignition on for a moment and then off. If applicable, wait one minute for the illuminated entry lamps to turn off.

Connect the voltmeter and read the voltage.

Test Conclusion

The current reading (current drain) should be less than 0.05 amps. If it exceeds 0.05 amps after a few minutes, and if this drain did not show in previous tests, the drain is most likely caused by a malfunctioning electronic component. As in previous tests, remove the fuses in interior fuse junction panel one at a time to locate the problem circuit.

Generator On-Vehicle Tests

Troubleshooting or diagnosis is required before actual service can be made in the electrical system. Even where an obvious condition makes replacement of a component necessary, find out why the component failed. When a condition is diagnosed correctly, unnecessary service is prevented, the time the vehicle is out of service will be decreased, and the condition will be properly corrected the first time.

In order to check the charging system, the use of Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent tester is suggested.

When performing charging system tests, turn off all lamps and electrical components. Place transmission in neutral and apply parking brake.

CAUTION: Do not make jumper wire connections except as directed. To do so may damage generator (GEN) (10346).

CAUTION: Do not allow any metal object to come in contact with the housing and internal diode cooling fins with key on or off or short circuit will result and burn out diodes.

NOTE: Battery posts and cable clamps must be clean and tight to ensure accurate meter indications.

Load Test

Switch the Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent to the ammeter function.

Connect the positive and negative leads of the Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent to the battery (10655).

Connect the current probe to the generator B+ output lead, Circuit 38 (BK/O). On Mitsubishi 215 ampere generator, use Circuit 605R.

With the engine running at 2000 rpm, adjust the Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent load bank to determine the output of the generator. Generator output should be greater than the graph shown below. If not, refer to the Symptom Chart in the Diagnosis and Testing portion of this section for diagnostic procedures.





No-Load Test

Switch the Rotunda Alternator, Regulator, Battery and Starter Tester (ARBST) 010-00725 or equivalent to the voltmeter function.

Connect the voltmeter positive lead to the generator B+ terminal and the negative lead to ground.

Turn all electrical accessories off.

With the engine running at 2000 rpm, check the generator output voltage. The voltage should be between 13.0 and 15.0 volts. If not, refer to the Symptom Chart in this section for diagnostic procedures.

Generator Bench Tests (Integral Rear Mount Regulator, Internal Fan Generator)

NOTE: The integral rear mount regulator � internal fan type generator (GEN) (10300) is serviced as an assembly only.

Replace generator as required after performing generator on-vehicle tests. Refer to Section 14-02B.

Capacitor

The radio voltage regulator capacitor (18832) connected across the heat sinks may be tested on a capacitor tester if available. Its value is .158 MFD, and 100 working volts DC.

In the absence of a capacitor tester, the unit may be checked for shorts by means of an ohmmeter connected across the terminals. A reading under 20 milli-ohms indicates a shorted or leaking radio voltage regulator capacitor which should be replaced.

Sorry, just now got on here again. Replaced the alternator this morning and so far so good. Keeping my fingers crossed. No more voltage fluctuating all over the place. I will drive it some more and follow up. Thanks.

Well, the alternator still works good. Only fluctuation comes when I turn on the heat/air. It sounds like it is coming from the dash underneath the ac/heat controls, I hear a click then a buzz and the voltage gauge on the dash drops. If I have enough other things going (radio, windshield wipers, headlights and pressing the brakes), then the voltage will drop enough to make the transmission shift late. Not as hard as limp mode, but noticably harder than normal. Could this click and buzz be a ground problem? Where do I need to look?

Thanks