1995 BRONCO XLT Check Engine Light / Sensors

Hi Guys !

My BRONCO is a 1995 XLT with a 351FI Windsor engine.

I need some help here with a " Check Engine " light issue.

I replaced my computer with a remanufactured computer earlier this spring, because we were getting multiple error codes, which couldn't be cleared. 

After replacing the Computer everything seems to be working correctly, ........ except ...... the check engine light.

I have had a thorough diagnostic test performed on my BRONCO, and ended up replacing one sensor.

ALL faults were cleared from the computer and the diagnostic test said that I had no more bad sensors.

I have checked all of the connectors to all the sensors and they appear to be in good condition.

Still have that damned " Check Engine " light on.  I know there are many who will tell me to just ignore that light, but I can't. 

If the light is on ..... something is wrong !  ( I can't help it being an IT and Telecommunications Engineer for 30 yrs. )

As I said above, we cleared every " Fault " from the computer, but the " Check Engine " light kept coming back on.

What is my next step to clearing the " Check Engine " light and getting it to turn off ?

I know this is an older vehicle, but I am trying to restore this truck to as " Cherry " as I can afford to do.

Turning off the " Check Engine " light by pulling a fuse or cutting a wire isn't a solution, so I hope no one suggests that move.

Yo WingWalker,

Do you recall what the code was?

Sometimes a code does not necessarily come up due to a bad sensor or other component. For instance, DTC 121, 122, 123, 124, 125 in TSB 94-26-4; "...The following is a list of vehicle symptoms which have been associated with the TPS, but can also be related to other vehicle components. Check engine light, Stalls, quits, hesitation/stumble, fast idle; To minimize the replacement of good components, be advised that the following non-EEC areas may be the issue: Excessive blow-by, PCV malfunction, Vacuum leaks, Fuel pressure, Throttle sticking or linkage binding..."

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19 @

http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded

Some basics;

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 including Reverse.

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

Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First

Post Code(s) here according to:

KOEO

&

KOER

GL!

I think you might have missed some of my comments. 

I CLEARED all my codes after replacing the Computer and several Sensors.  NO More Codes to read !

Just " Check Engine " Light is left.  There are NO MORE Codes to read.

Yo,

I read it, but memory codes are problems that the computer has noticed in the past. If for example there was a loose wire to a solenoid that only lost contact while driving but was making contact while testing the system there would be No hard fault code. The same would happen for a sensor that only went out of range occasionally.

Occasionally is the key word; Ford also describes it as an "intermittent condition".

So, I suggested another self test because I do not know the time-lines between the "thorough diagnostic test" & clearing codes, sensor replacement, etc.

If the shop did the "thorough diagnostic test", then I would have hoped that they would have diagnosed and eliminated the CEL LIT with no code condition.

Do you know what to check with a CEL lit while driving, but no codes are detected? I will find it later and post it here. It involves testing at the PCM, its connector, various components, etc.

Do you recall what the code was or the sensor that was replaced?

...

How to Clear the Continuous Memory

Note: Do not disconnect battery to clear Continuous Memory. This will erase the Keep Alive Memory (KAM) information which may cause a driveability concern.

Run the Key On Engine Off Self-Test.

When the DTCs begin to be displayed, deactivate Self-Test:

STAR Tester: Unlatching the center button (up position).

All others: Remove the jumper wire from between Self-Test Input (STI) connector and the Signal Return Pin of the DLC.

Scan Tool: Pushing the STOP button.

Continuous Memory will be erased in the PCM.

...

Wiggle Test Special Note:

The technician can attempt to re-create & detect an ntermittent fault using the Wiggle Test procedures.

Key On Engine Off Wiggle Test Procedure:

Hook up a STAR Tester, VOM or Scan Tool.

Turn the ignition key to the ON position.

For STAR Tester or VOM, activate, deactivate and reactivate Self-Test to enter Continuous Monitor Diagnostic Test Mode (DTM). For Scan Tool, enter DTM, then enter wiggle DTM.

*** BEWARE OF FAN, HOT ENGINE, HOSES, BELTS, PULLEYS ***

Tap, move, and wiggle the suspect sensor and/or harness. When a fault is detected, a Continuous Memory DTC will be stored in memory and indicated as follows:

STAR Tester: Red LED lights and/or continuous tone.

Malfunction Indicator Lamp (MIL) aka CEL: Lights

VOM: Needle Sweep

Transmission Control Indicator Lamp (TCIL) on E4OD

Scan Tool: Continuous Tone

Engine Running Wiggle Test Procedure

Special Note:

The Engine Running Wiggle Test may be activated any time the engine is running.

Hook up a STAR Tester, VOM or Scan Tool as shown.

Key off.

Start the engine.

For STAR Tester or VOM, activate Self-Test, deactivate and reactivate Self-Test to enter Engine Running Continuous Monitor DTM. DO NOT shut the engine off. For Scan Tool, enter DTM, then enter wiggle DTM.

Tap, move, and wiggle the suspect sensor and/or harness or drive the vehicle. *** Especially at the sensor that was replaced.***

When a fault is detected, a Continuous Memory DTC will be stored in memory and indicated as follows:

STAR Tester: Red LED lights and/or continuous tone.

Malfunction Indicator Lamp (MIL): Lights

VOM: Needle Sweep

Transmission Control Indicator Lamp (TCIL)

Message Center (Continental Only)

Scan Tool: Beeps

What is a " CEL LIT " ?

What is a " STAR TESTER " ?

I print all these things out and take them with me to the shop.  Anything to help out the mechanic.

As to what sensors were replaced, I'll get back to you on that.

As for having the truck warmed up and all ready for tests, that  isn't an issue.  By the time I get to the shop, everything is all warmed up and ready for tests.

CEL is Check Engine Light. Lit is what you are experiencing now.

Star Tester aka NEW GENERATION STAR (NGS) TESTER DIAGNOSTIC TOOL was the factory scan tool for years @ all Ford Service departments. It was replaced in 2006, however there are 1000's of NGS still in use & available used on E bay, Craigs list, etc.

You're welcome!

No Codes, but CEL IS LIT.

Note that the computer is the POWERTRAIN CONTROL MODULE (PCM), aka ELECTRONIC ENGINE CONTROL, (EEC), EECIV FOR YOUR YEAR.

Check Battery voltage, must be above 10.5 volts.

•Replace battery if not.

•Check battery connections, corrosion, ground faults, and wiring.

• Fix all wiring.

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

•Inspect wiring and connector, Replace Alternator if not.

•Any recent voltage irregularities from electrical charging system can cause failures.

•Check fusible links on Starter Solenoid if equipped.

•Check fuses and surge protection diode in under hood Power Distribution Box.

•Replace any fuses, diodes, and links if needed.

•Check EEC relay, must show battery voltage when engaged.

•Replace relay and damaged wiring if not.

•Make sure pin 30 on the computer is hooked up correctly.

•Manual transmission computers need to sense SIG-RTN on pin 30 when in neutral.

•Automatic transmission computers need to sense Ground on pin 30 when in neutral.

•E4OD need an operational Manual Lever Position Sensor (MLPS)

•Check aftermarket devices like alarm system connected to engine or computer components.

•Restore engine and computer system to original configuration.

•Check aftermarket computer chips and other plug in controls.

•Any chips or controls that impede basic engine and computer function need to be removed.

•Restore computer and harness to original configuration.

•Disconnect computer and inspect for damaged or pushed out pins, corrosion, loose wires.

•Replace computer if visually damaged, repair any damaged pins in harness. Check foe leaky capacitors.

•Visually inspect the ENTIRE engine and computer wiring harness and connections for corrosion, ground faults, shorts, physical damage, and general condition.

•FIX ANY & ALL PROBLEMS

•Check Self-Test Input circuit on Pin 48 at computer harness for shorts to ground.

•Replace faulty wiring.

•Remove check engine light bulb and check Self-Test Output circuit for shorts to ground.

•Replace faulty wiring.

•Measure resistance between battery negative post and pins 20, 40, and 60 at the computer harness.

•Resistance must be less than 5.0 ohms.

•Replace faulty wiring between computer and battery if not.

•Turn key to ON with engine OFF and computer removed. Measure voltage on pins 1, 37, and 57. Must be above 10.5 volts and within 1.0 volt of each other.

•Replace faulty wiring between computer and battery if not.

•Turn key ON with engine OFF and computer reinstalled. Measure voltage between Pin 26 and 46 (voltage reference and signal return) must be between 4.0-6.0 volts.

•Replace faulty wiring and sensors.

•Measure resistance between Pin 46 and Pins 40 and 60 at the computer harness, must be less than 5.0 ohms.

•If all the wiring and sensors check out, Replace the computer.

....

EEC IV Connector Pin LEGEND, Bronco @ http://web.archive.org/web/20120118104425/http://www.oldfuelinjection.com/truckpinouts.html

EEC IV CONNECTOR PIN DIAGRAM @ http://web.archive.org/web/20120115055623im_/http://www.oldfuelinjection.com/images/eec04.gif