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Discussion Starter · #1 ·
These are the diagnostic codes I'm getting after my 92 4runner check
engine light started up last night. Are there really 2 unrelated
things that happened to go at precisely the same instant, or does this
indicate a third, bigger problem? The vehicle is running fine. I'm
worried that my ECU is causing all of this, and I'm not bright enough
to do electrical diagnoses

21=
OXYGEN SENSOR SIGNAL/OXYGEN SENSOR HEATER SIGNAL

OPEN OR SHORT IN OXYGEN SENSOR OR OXYGEN SENSOR SIGNAL

43=
STARTER SIGNAL--NO "STA" SIGNAL TO ECU UNTIL ENGINE SPEED EXCEEDS
800RPM

--IGNITION SWITCH/CIRCUIT

--ECU
 
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Discussion Starter · #2 ·
"Joe" <[email protected]> wrote in message
news:[email protected]
> These are the diagnostic codes I'm getting after my 92 4runner check
> engine light started up last night. Are there really 2 unrelated
> things that happened to go at precisely the same instant, or does this
> indicate a third, bigger problem? The vehicle is running fine. I'm
> worried that my ECU is causing all of this, and I'm not bright enough
> to do electrical diagnoses
>
> 21=
> OXYGEN SENSOR SIGNAL/OXYGEN SENSOR HEATER SIGNAL
>
> OPEN OR SHORT IN OXYGEN SENSOR OR OXYGEN SENSOR SIGNAL
>
> 43=
> STARTER SIGNAL--NO "STA" SIGNAL TO ECU UNTIL ENGINE SPEED EXCEEDS
> 800RPM
>
> --IGNITION SWITCH/CIRCUIT
>
> --ECU
>

I don't think the two codes are related unless someone or something has
disturbed a wiring harness between those components and the ECU. ECU
failures are very rare. Since you happen to have a short or open in 2
different components, I'd check the O2 sensor before replacing it.
--
Ray O
correct the return address punctuation to reply
 
G

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Discussion Starter · #3 ·
well today sometime after doing the diagnostics the check engine light
went off. Maybe it was all a bad dream.
 
G

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Discussion Starter · #4 ·
"Joe" <[email protected]> wrote in message
news:[email protected]
> well today sometime after doing the diagnostics the check engine light
> went off. Maybe it was all a bad dream.
>

I believe both of those codes have a 2 trip detection logic. If you take 2
good trips without the ECU sensing the fault, it turns the check engine
light off.
--
Ray O
correct the return address punctuation to reply
 
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