Hey guys....I have a 96 Blazer 4 door 4x4, 4.3, auto trans., approx. 210,000 miles.
Recently I've been getting a frequent SES light, and occasional stalling.
When I scan it I get P0112 and P1122, (sometimes one, sometimes the other, sometimes both), indicating a problem with the TPS circuit.
I have looked closely at the wiring harness and traced everything from the TPS to the PCM, all appears to be OK.
I own a Matco Determinator, and when I watch the TPS performance with the ignition on, engine not running, I get good results on both TPS Volts and position %.
The TPS response is smooth and consistent.
But when I run the engine while watching the TPS parameters on the scan tool, the TPS voltage is very low...~0.12 volts at idle. I can even see when it sets the code on the scan tool.
My confusion comes in when I check the voltage with a digital multi-meter.
I have two Fluke 787 Process meters, and I had one hooked up at the TPS watching the ref. volts. A good 5.0 was maintained during testing.
I had the other connected to the TPS signal wire at the PCM connector, watching the signal return voltage at the PCM.
Both meters were grounded at the TPS connector, Black wire.
According to the meter, the TPS signal return voltage as shown at the PCM is quite a bit higher than what's reflected by the scan tool, so my question is this: is it possible for the TPS to read good when the engine isn't running, but fail whenever the engine is running?
I have a new TPS ordered and it should be here tomorrow or Tuesday.
The old TPS in an AC brand, and may be the original for as far as I know.
For now I have adjusted the butterfly screw in 1/2 turn, just to keep the TPS from setting the code, and a lengthy 20 mile test drive, the truck is running OK and so far no SES light.
Sorry for the rambling post, but I'm just wondering if maybe my PCM is in the early stages of failure.
Thanks for reading, and I'd appreciate any input from those with insight.

 

I've gone down this path with a '96 before. When you have the right reading at the sensor track the ground wire back to the PCM and check the reading from there. If you get the same results you probably have a problem in the PCM (the '96's have a known ground problem). If you get different readings then examine the wiring carefully between the PCM and the sensor.

Luckily PCMs are not that expensive.

 

Thanks for the reply.
I'll recheck the wiring and pay particular attention to the grounds.
I have what I believe to be accurate wiring diagrams, so I at least have something to go by.
I'm going to replace the TPS in a few days and run another live data session with the Determinator, just to see if the new TPS reacts differently.
I should probably read up on PCM's and start shopping around, because I may need one in the near future.
Thanks a lot for your help.

 

If you have a spare TPS that's easy. I did that too. Here is the post where I was tracking down this and other problems. I think I bought my ECM from spareecm.com

There is also a harness update to fix the ecm ground problem is covered by TSB 667103. A google search will pull up the instructions.

Good luck.

 

Do you have any trans slip/no shift issues? Here's a TSB that applies to Bravada's (but more than likely transfers over to the blazer/jimmy's as well.

00-07-30-026 - (12/21/2000) Automatic Transmission 1-2 and/or 2-3 Upshift Slip/Flare, No 3rd or 4th gear, Launch Shudder (Revise VCM Wiring)
1996 Chevrolet and GMC C/K, S/T, M/L, G1, G2, P3 Models
1996 Oldsmobile Bravada
with VCM and 4L60-E (M30) or 4L80-E (MT1) Automatic Transmission

This bulletin is being reissued to ensure that correct procedures are followed for this condition. Please discard Corporate Bulletin Number 66-71-03A (Section 7 -- Automatic Transmission).

Condition
Some owners may comment that the automatic transmission has either a slip or flare on the 1-2 and/or 2-3 upshift, or no 3rd or 4th gear, or launch shudder. Upon investigation, the technician may find a DTC P1870 stored in the VCM.

Cause
A poor internal ground between the two circuit boards of the VCM may cause the VCM to command erratic line pressure at the pressure control (PC) solenoid valve.

Correction
Using harness jumper wire and instruction kit, P/N 12167310, revise the wiring harness at the VCM connector. Corrections were made to the VCM beginning 2/14/96. The corrected VCMs are identified with service number 16244210 on the VCM identification label.

Procedure
The following is a summary of the instructions included with the service kit:
1. Remove the negative terminal from the battery.
2. Move the wire located at connector J3 (WHITE/GREY/CLEAR), pin 18 to connector J1 (BLUE), pin 23.
3. Install the jumper wire between connector J2 (RED), pin 26 and connector J3 (WHITE/GREY/CLEAR), pin 18.
4. Install the tag included in the kit around the VCM wiring harness. This tag notes that the wiring harness has been modified.
5. Reconnect the negative battery terminal.

Road test to verify that the condition has been corrected. If any of the following conditions are noted, the transmission should be repaired or replaced using the most cost effective method. Canadian dealers should repair the transmission.
1. Transmission fluid oxidation or excessive sediment.
2. Transmission slip or flare after this service fix is performed.
3. DTC P1870 is stored on a 4L60-E (M30).

The following tools are available from Kent-Moore (1-800-345-2233) for use in removing and relocating the VCM wires:
1. J 41758 Terminal Tool; used to remove the wire from the VCM connector.
2. J 41759 Punch; used to punch a new hole through the connector seal.

Parts Information
Part Number: 12167310
Description: Harness Jumper Wire Kit
Qty: 1