What specifically triggers code 21? (searched)

[Doward]

TSRM is really vague, as it says it is either the heater circuit (that I can find no problems with) or it is 'During air-fuel ratio feedback correction, voltage output from the Oxygen Sensor does not exceed a set value on the lean side and the rich side continuously for a certain period.'

This tells me that for some reason, either my '88 turbo is staying rich (I have no code 26 thought) or that the O2 heater circuit has a problem I can't freakin' find.

Now, the strange thing is, I do not get this code all the time, but I can duplicate it with very high accuracy by doing the following:

1) Find long stretch of road
2) Cruise 60mph for at least 3-5 minutes
3) Suddenly punch 3/4 throttle
4) Curse as CEL illuminates.

The first time it happened, was on I75. If I never punch it and suddenly boost, I never get the damn signal.

So what exactly triggers the 21? Automatic turbo '88 here.

 

[drjonez]

you're looking @ the later TSRM.

code 21 is just o2 sensor signal. the older ECUs don't check the heater circuit, so code 21 just means that the feedback signal is either not getting to the ECU or it's not as expected. my $$ is on a dead O2 sensor. get a new one and see if that changes anything.

you also just try resetting the ECU and seeing what happens...

 

[Doward]

I'll check it out, but I gotta find my old analog voltmeter, lol... I cleared the ECM, thanks, Doc, as well for the info on the new/old... I'll dig out my '87 TSRM and read up on it, as well!

Thanks again, I'll scope it out and see what I find. 450mv ~ 14.7:1 afr on the Toyotas as well, right?

 

[Doward]

I don't have a scope, but I do have a decent little DMM... I'll see what I can get her to kick out for me

Just as a disclaimer - nobody get the idea that you can 'tune' with the narrowband O2... It will tell you 'Rich' or 'Lean' - but now how rich or lean.

Wideband ftw.

 

[Nick M]

A scope is even better and required for serious troubleshooting.

:word8kn:

The heated oxygen sensors are fused. If you have one. I remember a few that had blown a fuse. 4Runners, Camry's etc.