Flashing PCM

[GPFred]

Ok, here's some back ground. 2000 GP with 3.1 with 88K. New front O2 sensor, plugs, wires, 2 coil packs, CAT all in last 3 months. SES light keeps getting kicked on for low voltage to front sensor.

For those who have kept up with the O2 sensor woes on my GP, its the SES light again due to low voltage to the front sensor. Service tech tells me everything checks out and all sensors, electronics,etc are putting out proper signals and voltages after they ran another diagnostics. The O2 sensor had been replaced with another AC-Delco sensor. They are now telling me that it could be a latent signal from the PCM causing an occasional low voltage signal and that I should take it to the dealer and have them flash the PCM to clear the latency. To me this sounds bogus and they are guessing. Anyone have this before? What is flashing the PCM and how is it done? And can I do the flashing at home without paying the dealer $90 just to drive it in the door? Car runs great and gets good mileage, kicks well into passing gear MOST times, but once in a wihile bogs down and the light kicks on.

[BNaylor]

Originally Posted by GPFred

Ok, here's some back ground. 2000 GP with 3.1 with 88K. New front O2 sensor, plugs, wires, 2 coil packs, CAT all in last 3 months. SES light keeps getting kicked on for low voltage to front sensor.

For those who have kept up with the O2 sensor woes on my GP, its the SES light again due to low voltage to the front sensor. Service tech tells me everything checks out and all sensors, electronics,etc are putting out proper signals and voltages after they ran another diagnostics. The O2 sensor had been replaced with another AC-Delco sensor. They are now telling me that it could be a latent signal from the PCM causing an occasional low voltage signal and that I should take it to the dealer and have them flash the PCM to clear the latency. To me this sounds bogus and they are guessing. Anyone have this before? What is flashing the PCM and how is it done? And can I do the flashing at home without paying the dealer $90 just to drive it in the door? Car runs great and gets good mileage, kicks well into passing gear MOST times, but once in a wihile bogs down and the light kicks on.

I thought you had the problem resolved GPFred. Oh well.

Re-flashing or applying an update to the stock PCM is a proper corrective action that the dealer could undertake when all else fails but there is no guarantee it will fix your problem.

Re-flashing is when they use a Tech II machine and dump the contents of the KAM memory and firmware. Then they re-program a new updated software routine keyed to your model GP, options and VIN.

You won't be able to do it at home without a re-programmer kit like from Autotap or DHP.

If you've changed all those parts its hard not to rule out the PCM. You might try ohming out all control and ground wires from the 02 sensor to the PCM to rule out wiring for sure. I might have an old wiring diagram for the 3.1 and the 02 sensor circuit.




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[BNaylor]

Update to your problem:

Tools required: Multimeter

There are 4 wires going to the front 02 sensor connector plug. One is 12 v from the ignition circuit to the 02 sensor heater element. One is system ground. The other 2 wires feed the PCM directly as input signals.

H02S 1 Hi in and H02S 1 Low in

Pin out:

H02S Low = Pin A (tan wire) from 02 connector to PCM connector Pin 46

H02S Hi = Pin B (purple wire) from 02 connector to PCM Pin 45

You can ohm these lines out point to point and with connectors off check for short or any resistance to ground.

On the 02 heater voltage and ground:

O2 connector Pin D (pink wire) should be 12 volts (ignition must be on).

02 connector Pin C (black wire) is ground.


If nothing else you could at least rule out the wiring. After that the PCM may not be properly processing the H02S Low input since that corresponds to your DTC error code. Good luck!




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials[/quote]

[GPFred]

Thanks for the help, I will try that this weekend. I'm just a bit frustrated with this and having done all the mechanical things it had to be down to electrical. I was just hoping that the PCM is not involved as the cost is something I don't need at this point. had to replace a PCM on an old Taurus a number of years ago and it was close to $1000 then. Thanks again.

[jimmytroanoke]

While you are checking your voltages etc. do a "wiggle" test with the meter hooked up to find wires that may be broken in the harness.

[BNaylor]

Originally Posted by GPFred

Thanks for the help, I will try that this weekend. I'm just a bit frustrated with this and having done all the mechanical things it had to be down to electrical. I was just hoping that the PCM is not involved as the cost is something I don't need at this point. had to replace a PCM on an old Taurus a number of years ago and it was close to $1000 then. Thanks again.

No problem GPFred. It must be very frustrating. The last PCM problem I had took me two days to track down and it turned out to be a bad electrical connector. The PCM costs have gone down. We got one for a GM 3.4L V6 for $125.00 at the salvage yard. But it should come off the same year, model and engine size, etc.

Another suggestion would be to pull out the receipts/invoices and see what specific AC Delco 02 sensor was installed. Or check the markings on the sensor.

The parts directory shows GM part number 25312203 which should be AC Delco part number AFS109. But I recall the AFS109 is also the one the Series II 3800 uses. But I'm not sure thats correct because I found another GM part number specifically for cars equipped with a 3.1 from 99 - '02 which lists as GM part number 25318321.

If you were depending on the mechanics to get the parts, it may not hurt to double check everything. Let us know how it turns out.




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials