Code 40

Ok, so the bronco has been running great since I put on the new/correct computer. So far two days in a row, the check engine has come on. Yesterday the code was lost when I shut it down, but today I caught it before shutting down!!! 40. From what I've found is the rear O2 sensor is bad. Correct me if I'm wrong.....there's only one prior to the cat. Please tell me I'm wrong. Really don't want to replace this computer too!!!!!

Thanks

Yo Justin,

Are you using a code reader or did you do the self test by BroncoJoe19?

The number 40 is not a DTC, it is most likely from the Cylinder Balance Test;

-Immediately after all KOER codes have been output, a quick tap of the throttle will initiate the cylinder balance test.

-The codes shown are of a slightly different format, that is, they are multiples of ten. 10, 20, 30, 40, etc. for example 4 flashes would equal 40.

So, Cylinder #4 Failed Cylinder Balance Test.

Check for usual suspects; loose/bad spark plug or wire @ plug or @ distributor, or distributor terminal fouled or carbon tracks inside cap, etc.; then inspect cylinder 4 injector connector, mine loosened due to a squirrel dinner.

...

BTW;

I believe there is only one O2 sensor on your 90 and it is on passenger side (bank 1).



HEGO (O2 sensor) Connector C114 Location Diagram in a 90 by Ford via Seattle FSB

More diagrams @ http://www.supermotors.net/registry/20487/76450

Such as HEGO Ground,



Ground Locations in a 90 from 1990 Bronco EVTM; G100 LH side of Radiator support G101 RH side of Radiator support G102 RH side of Radiator support

*** G103 LH rear side of engine, near knock sensor ***

G104 LH rear side of engine compartment, near electronic engine control (EEC) module, on the left fender close to the firewall G105 LH Side of engine G106 RH fender apron, near voltage regulator G107 RH fender apron, at starter relay G108 RH fender apron, at voltage regulator G109 RH fender apron G201 LH rear side of I/P (looking at the diagram it is at the bottom of the driver's side dash assembly. Screwed to the bottom edge, just to the left of the steering column. It is the ground for the instrument cluster) G202 Behind RH cowl panel G203 RH rear side of radiator support G204 On steering column G205 Behind Center of I/P (Dash), near speed control amplifier G400 LH side of cargo area, near rear light assembly G401 Below LH side of cargo area, near crossmember G500 Inside driver's door, near left door speaker.

by our pal

by BroncoJoe19 (Joe) at Ford Bronco Zone Forums

Using a code reader. Preformed the test, once all codes generated, tapped throttle, and nothing. Only code was idle too high. But checked the wiring, all is well. A glitch perhaps. But in a week or so I'll be taking on an 8-9 hour road trip and shall see how it does.

Yo,

OK.

What brand & Model number is the reader?

Innova 3145

Yo,

Page 32

Retrieving Codes

KOER SELF TEST (EEC-IV SYSTEMS)

33 Chapter 4

1. Warm up the vehicle to normal operating temperature. ■ Start the engine, increase engine speed to 2000 RPM, and maintain engine speed for approximately two to three minutes. In most cases, this is sufficient to allow the engine to warm up to normal operating temperature. NOTE: Failure to warm engine to normal operating temperature before performing KOER test might result in a false Fault Code being sent to the code reader.

2. Turn ignition off.

3. Turn the Code Reader off (press the ON/OFF button, as

necessary), then connect the Code Reader to the vehicle's

test connectors.

■ Both the large and small connectors must be

connected.

4. Turn ignition on and start the engine.

5. Press and release the ON/OFF button to turn the Code Reader

"ON". ■ Three zeros should be visible on the display at this time.

6. Press and release the TEST/HOLD button to put the Code Reader in Test Mode. ■ A square icon (on the right-hand side of the screen) displays and flashes each time the Code Reader receives a code. The code is then shown on the Code Reader’s display.

■ A small “R” is shown in the upper right-hand corner of the display to indicate that the code being received is a KOER Self Test Fault Code.

*** 7. The first code displayed by the code reader is the Cylinder Identification (ID) Code. ■ The cylinder ID code identifies the number of cylinders of the vehicle that is under test. NOTE: If code 98 or 998 displays instead of a cylinder ID

code, the vehicle is operating in "Failure Mode". The computer

goes into failure mode when it detects a signal from a sensor

that indicates the sensor has failed and is completely out of

specifications. The computer substitutes a fixed signal value

for the failed sensor to keep the vehicle running. Failure

mode codes 98 or 998 are usually accompanied by one or

more Diagnostic Trouble Codes that indicate the failed

sensor. A vehicle operating in failure mode is operating at

a minimal level, and the faults that are causing these

Diagnostic Trouble Codes to set must be repaired as soon

as possible.

8. Check your vehicle's service manual to see if your vehicle

is equipped with a Power Steering Pressure Switch, Brake

On/Off (BOO) Switch and/or an Overdrive Cancel Switch.

If your vehicle is equipped with these features, perform

the following immediately after retrieving the Cylinder ID

code (step 7).

NOTE: If you are unsure of your vehicle's equipment, it is

recommended that you perform these procedures anyway.

■ If your vehicle has a Power Steering Pressure Switch...metc.

Ran all procedures that the book calls for, cannot get code 40 to pop up. Either a glitch or something was loose that I missed or I mistakenly corrected. Drove around all day today without the slightest issue.

Yo,

Great!

Thanks for the update Justin!