Re: 2001 Silverado OBD codes?


"zxcvbob" <zxcvbob@xxxxxxxxxxx> wrote in message
news:4k4s90Fag3ojU1@xxxxxxxxxxxxxxxxx
Mike wrote:
"zxcvbob" <zxcvbob@xxxxxxxxxxx> wrote in message

My OBD2 reader got here today and I just checked it. The DTC code is
P0300, which means random misfires. It also has a pending code of
P0300. I printed a report and to my untrained eye everything looks OK,
/except/ the fuel trim numbers:
STFT - Bank 1 2.34%
LTFT - Bank 1 2.34%
STFT - Bank 2 -8.59%
LTFT - Bank 2 -5.47%

Should I just reset everything back to zero and see what happens? Maybe
the bank 2 fuel trim is causing the misfire? Why so much variance
between short term and long term?

There's not a whole lot to the ignition system that I can check. Each
plug has its own ignition coil, so the high-tension wires are very short
and direct. I haven't pulled any sparkplugs yet.

I haven't seen an engine in many years with so few vacuum hoses. I
should take the cover off the throttle body and check the hoses.


Take a look at your O2 sensor values, especially bank 2. The O2
sensors should be switching between .1 volts to .9 volts, with .1 being
lean and .9 being rich. If the bank 2 sensor is failing it may be staying
on the rich side. This would cause the ECU to remove fuel on bank 2 as
indicated by the long and short term fuel trim. If bank 2 is being run
too lean this may be be the cause of the P0300 code as a lean fuel
mixture is harder to ignite.


I don't have an O2 tester nor an oscilloscope. The diagnostic tool just
says the O2 sensor monitor and O2 sensor heater monitor are "complete" and
the fuel system status 1 and 2 are closed loop.

OK. I thought you had a scan tool, not just a code reader.


Would it be worthwhile to swap the banks 1 and 2 O2 sensors and see if the
problem follows the bank 2 sensor?

That would work but it may not be possible. Some of the connectors are
keyed differently and the wires may be a different length also. If it is
possible to switch them go ahead and do so and see if the problem follows.
Another thing to try would be clear the codes, disconnect bank 2 and see if
it runs any better and see what codes you get.

If you have a multimeter and a wiring diagram you can also check the O2
voltage. The O2 sensor generates it's own voltage. With the wiring diagram,
locate the O2 sensor output wire ( signal to ECU ) and back probe it with
the red lead from the meter ( black lead goes to a GOOD ground ). Set meter
to dc voltage scale, start engine and read sensor voltage. The sensor may
need to warm up for a few minutes before it starts switching. It should
switch voltages rapidly from a high to low voltage. It should not go below
..1 volt or above .9 volt. If it switches very slowly or stays either high
or low constantly it may have failed.

You must also be aware that the O2 sensor may be reading correctly when
stuck high or low if other problems exist. For example, a vacuum leak would
cause a lean condition which would cause the O2 sensor to read lean. A rich
condition, such as a leaking injector, would cause the O2 sensor to read
rich.


This engine has 4 O2 sensors; 2 before the catalytic converter and 2
after. Is the one before the converter is to monitor that half of the
engine and the one after to monitor the catalytic converter?

Yes, that is correct. The front sensors ( sensor 1 ) control the air/ fuel
mixture. The rear sensors ( sensor 2 ) are used to monitor catalyst
efficiency.


Can a place like Autozone check the sensor voltages and waveform?

As far as I know they only have code readers.


Thanks,
Bob


.

Relevant Pages

  • Re: 2001 Silverado OBD codes?
    ... I printed a report and to my untrained eye everything looks OK, /except/ the fuel trim numbers: ... STFT - Bank 1 2.34% ... The diagnostic tool just says the O2 sensor monitor and O2 sensor heater monitor are "complete" and the fuel system status 1 and 2 are closed loop. ...
    (rec.autos.tech)
  • Re: 1991 Camry 2VZ-FE Engine; CO Emission Failure
    ... Part of the sensor is exposed to atmosphere, ... what produces the voltage. ... the exhaust stream and the difference in content is small. ... a fuel trim trend that averages out to be stoichiometric mixture. ...
    (alt.autos.toyota)
  • Re: 1991 Camry 2VZ-FE Engine; CO Emission Failure
    ... Part of the sensor is exposed to atmosphere, ... what produces the voltage. ... the exhaust stream and the difference in content is small. ... a fuel trim trend that averages out to be stoichiometric mixture. ...
    (alt.autos.toyota)
  • Re: Code....PO138 02 (Circuit High...........
    ... 02 Circuit High ... it's the bank on the passenger side of the vehicle. ... Sensor 2 would be the one downstream in the exhaust (towards the rear for a non-transverse engine. ... It's telling you that that O2 sensor has high voltage - probably bad sensor, or might be problem in the cable to the sensor. ...
    (rec.autos.makers.chrysler)
  • Re: Code....PO138 02 (Circuit High...........
    ... 02 Circuit High ... it's the bank on the passenger side of the vehicle. ... Sensor 2 would be the one downstream in the exhaust (towards the rear for a non-transverse engine. ... It's telling you that that O2 sensor has high voltage - probably bad sensor, or might be problem in the cable to the sensor. ...
    (rec.autos.makers.chrysler)