> > wrote in message
> ups.com...
>
>> 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?
>>
> Jeff Strickland wrote:
> 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.


--
-Fred W