My son has a 98 Escort GT. 2.0, the check engine light has been on
for a while with the code P0141 02 Sensor Heater Circuit Malfunction
(Bank 1 Sensor 2), but the car still ran ok. Just recently the car
started fine and he drove about 1/4 mile and the engine quit, it would
not accelerate. Once the car cooled off it would start again and do
the same thing. I checked the codes again and an additional code was
there (PO136), which was the 1st o2 sensor. I changed the 1st sensor
and the code went away, but the car still has the same problem it
shuts off after a 1/4 mile or so, the 2nd code is still there. If I
change the 2nd sensor will this fix the problem or could something
else be causing the car to stop?
The HEATER CIRCUIT MALFUNCTION error means that the built-in heater inside
the sensor has failed. The only recovery from this is to replace the
affected sensor. Having said that, this is not an error that should result
in your car shutting down.
The sensor works when it has reached a certain temp. This temp will easily
be reached through the passing of the exhaust stream, but the rise-time is
too slow. The computer wants to see a valid input faster than exhaust stream
will heat the sensor -- the problem here is that the sensor is needed to
reduce smog, and a cold sensor will not reduce smog so they heat it by
internal means to get it to work. The internal heater is broken.
Neither code you reported should shut the car down. Of the two, the second
might result in the car reverting to Limp Mode, where it runs crappy -- and
rich (too much gas is fed).
Adding to what Jeff has mentioned, the first O2 sensor is the one used
to tell the ECU what the exhaust mixture is, and thereby allow it to
trim the fuel injection for the proper richness. The secind sensor is
only used on 1996 and later OBD2+ cars to tell the ECU how well the
Catalytic Convertor is cleaning up the final emmissions.
So the engine should run just fine with a bad 2nd sensor, it would just
throw check engine codes.
The fact that the car runs for a few minutes and then craps out is
consistent with your O2 sensor problems. The engine starts and runs
"open loop" for a few minutes until the ECU figures the O2 sensor should
be up to temp. At which time it tries toi use the sensors feedback to
adjust the fuel injection for optimum mixture.
I don't believe that the O2 sensor has sufficient 'authority' to change the
mixture enough to cause the car to stop running.
I had a situation once where a mechanic destroyed the threads in the
manifold while attempting to replace my oxygen sensor.
I had to drive the car for 3 weeks with no oxygen sensor and a plumbing plug
stuck in my exhaust manifold. My mileage went down by about 10% but the car
ran just fine. 1984 318i L-Jetronic.
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