Check Engine Light Won't Reset... (1 Viewer)

[Hltoppr]

While I have a feeling what the answer is, I thought I'd get some more input...

1992 FJ80, 197,500 miles.

Check engine code 21, Number 1 oxygen sensor comes up.
I replaced #1 with a new OEM sensor...

Removed the EFI fuse to reset the code....

Immediately get code 21 again.

Just cuz' I had one from CDan lying around...Replaced the other O2 sensor with OEM new.

Removed the EFI fuse....for a few minutes...

Immediately get code 21 again...


Anyone have any clue as to what would cause the code to not reset?


-H-
(Waiting for the answer that will probably make me go.... )

 

[PHAEDRUS]

oxygen sensor heater??????
not that I am smart I just went to the 3FE site and pulled it down.
Dave

 

[Hltoppr]

Anyone else care to take a guess?

-H-

 

[sixsracing]

Check the wires between the O2 sensor and the harness. If no visible problems then you'll be disconnecting the ECU and the O2 sensor at the plug and taking continuity/resistance readings between the two ends. If nothing shows up then try another O2 sensor, (new OEM can be bad). If that doesn't do it your either looking at a new/used ECM or a false code that was tripped by something else. How was the connector when you replaced the first O2 sensor? Have you tried disconnecting the battery yet? I know you pulled the fuse but I have had that method screw me once or twice.

 

[stayalert]

second that thought on the harness. On my truck there was lots of corrosion and heat etc. in the area of the sensors...Good luck. Another thought is that It may take several cycles or some time to clear....I blew a code during some heavy towing a few years ago. I had blown out an o2 sensor....I replaced the offensive pipe where the sensor was mounted was and re-used the original o2 sensor. I never determined what the code was but it cleared itself after a few days of normal driving....My friend and I resolved that the engine was just showing disgust at having to tow the trailer with an old landrover on it....Rob M Concord, MA

 

[1newlexus97]

I'd distconnect the negative terminal on the battery for 30 min. That's done it for
me in the past.

 

[Hltoppr]

I'll give it a try tonight....

-H-

 

[Hltoppr]

Disconnected the battery for about an hour this evening....

CE light still on with code 21....

Gonna go through the FSM to see if there's any info.

Any other ideas would be appreciated.

-H-

 

[landtank]

Does the light come on immediately when you turn the key on or after a drive cycle?

 

[toddslater]

I go along with stayalert and sixsracing, sounds like a harness issue. While this https://forum.ih8mud.com/showthread.php?t=36206 may not be exactly what your experiencing, it does touch upon harness issues and is a good thing for all 3FE owners to keep on file....I'm just glad David went through this first.

 

[Hltoppr]

Will litigate for ECU....

Thanks all!

I went ahead and pulled the neg. cable last night for about 45 min. No change.

Thus, I went ahead and did the check on the FSM troubleshooting tree.

Engine at op. temp., 2500 rpm for 120 seconds prior to test. Jump E1 and Te1 diagnostic ports....

Read voltage change between the two leads....No changes or pulses in 10 seconds. (Did this several times just to make sure...)

FSM says....REPLACE ECU.

Bummer.....

ANYONE HAVE AN EXTRA 1992 ECU SITTING IN THE GARAGE FROM A CONVERSION?

-H-

 

[sixsracing]

Make sure you check all the grounds you can find for that ECU. An improperly grounded ECU can and will give a false positive on this type of check. I have gone to the trouble of running a jumper cable from the battery to the ground on the ECU and the actual case of it also and have changed the results.

 

[Hltoppr]

Thanks, I'll probably pull the ECU this weekend!

-H-

 

[Hltoppr]

Hmmm.....

Well, it's not the ECU. I procured a friends 1992 ECU and popped it in....got the same code after about 20 minutes.

Started checking the wiring from the #1 O2 sensor....
Guess I've got some work to do this weekend.



-H-