914-SHO PCM code issues

[3d914]

As a result of my recent motor bench test, I got some CEL codes. With bruso's help we were able get codes to try and isolate the issues. Here's what we got: 26, 51, 95, & 65.

I started with Code 65 - Check intermittent HO2S (signal or ground). Remember I'm running a 3.2L with the 3.0 PCM, so can any guess what the problem might be? Yep, I have 4-wire O2 sensors for the 3.2 connected into the 3.0 component harness that was designed for 3-wire O2 sensors. (DUH! smiley here)

It appears that the three of the wires are similar between the two styles, but the 4-wire has an added signal return (GY/R). So the question is - can the four-wire be made to work as three-wire or do I just replace them?

TIA

 

[Phoenix]

I would grab MTX O2 and call it a day , save yourself the headaches.

 

[kevinspann]

I recall reading that the 4 wire ones won't work...not sure if they can be repinned to work or not. Easiest solution is getting MTX 02s.

 

[rubydist]

you need to get the 3-wire o2 sensors.

 

[rubydist]

26 isnt on my list of codes...

51 says the ect sensor is open and reading -40F. since it likely isn't that cold in your garage, most likely you have a bad connection on that.

95 is fuel pump secondary circuit failure, which usually gets set from an engine stall event and can almost always be ignored.

 

[3d914]

OK, 3-wire O2's it is. Now on to the next one (Long). Hope you guys like a challenge.

Code 95 - FP ground circuit (Fuel pump: open, bad ground or always on; bad fp ground or open between fp and pin 8 (FPM) at PCM)

I'm tracing this from the FP relay in my custom CCRM (schematic is here). I'm using change-over type relays and ignoring the normally open side (87a). So I have relay input at 30, switched output at 87, coil input at 86, and coil output at 85.

The input/outputs for FP relay are as follows:

• CCRM #12 = B+ Pwr In (30)
• CCRM #5 = FP Pwr Out when relays closes (87)
• CCRM #18 = Gnd from PCM & output for relay switch (85)
• CCRM #24 (PCM Pwr) = FP relay switched input power (86)

The first three tested fine out to their destinations. I then checked the coil input (86). It and both Hi/Low fan relays get their coil input from CCRM #24 - Vpwr, so they're all ganged together. When I trace #24 it tracks correctly to the following components:

• MAF (red)
• Fuel injectors (red)
• IMRC (red)
• PCM #37 (red) Vpwr
• PCM #57 (red) Vpwr
• Don't use Canister Purge or EGR

But as I went around through all the other sockets in the PCM connector to see if there were any shorts, I was getting a signal also on the following:

• PCM #9 - MAF Rtn
• PCM #16 - Ignition Gnd
• PCM #17 - STO/MIL (+12v)
• PCM #19 - FPM Gnd
• PCM #20 - Case Gnd
• PCM #30 - CPP
• PCM #40 - Power Gnd
• PCM #49 - O2 Gnd
• PCM #60 - Power Gnd

Now I could see them all being ground sides of circuits or power sides, but both? I must be missing something somewhere. Also, I can't tell whether #9 & #30 are positive or ground.

Edit: There is one thing that's odd though. I'm not using the stock Constant Control Relay Module (CCRM), so I came up with my own custom one. Since I don't have a schematic for the 3.0L PCM's CCRM, I've had to improvise with the 3.2L CCRM diagram. There's one case where a diode is used to prevent a ground circuit from flowing back into the relay coil inputs for several of the relays. Since I haven't added that particular relay into the circuit yet I didn't bother with the diode, but I suspect it may be needed anyway. I think it's more than coincidence that the failing sensors tie through the same grounding circuit where that diode was used.

 

[3d914]

Just for future reference. The 95 SHO and the X2J PCM I'm using is based on 3-digit codes, not two as I originally thought.