2005 PCM problem?

[GeorgeLa]

I need a recommendation for PCM repair. I’m getting P0628 low voltage at fuel pump. I can turn the fuel pump on by taking the fuel pump relay out of the TIPM and applying 12 volts to the fuel pump through the relay socket.

The schematic I have seems to be wrong? The schematic shows relay pin 85 going to Run-Start F951 through PTC no. 1 and relay pin 86 going to the PCM. When I put a voltmeter on the TIPM sockets for those pins, I get the socket for pin 86 going to ground and the socket for pin 85 going to the PCM.

When I measure the voltage output from the PCM at the relay socket, I get .8-.9 volts output to the fuel pump relay from the PCM. I get 0 ohms resistance when measuring from the PCM connector to the relay input socket in the TIPM.

I sent the PCM out for repair. Got it back, installed it and still P0628. PCM still needs repair? Maybe TIPM problem (doesn’t seem likely given continuity from TIPM to PCM connector.

Any recommendations for where to send my PCM for further testing?

 

[Ozymandias]

Stupid question, but did you change the relay itself in the process?

 

[Topzide]

It sounds like its the TIPM is the issue. The PCM only sends a trigger to the TIPM to send voltage to the fuel pump. Batteries fully charged and load tested? @Ozymandias just beat me to that. Check for any wiring issues along the way also.

 

[petersonj]

The schematic I have seems to be wrong? The schematic shows relay pin 85 going to Run-Start F951 through PTC no. 1 and relay pin 86 going to the PCM. When I put a voltmeter on the TIPM sockets for those pins, I get the socket for pin 86 going to ground and the socket for pin 85 going to the PCM.

Just to answer this question. Pins #85 and #86 are just to the coil of the relay. It does not matter if they are reversed.

- John

 

[Ozymandias]

It sounds like its the TIPM is the issue. The PCM only sends a trigger to the TIPM to send voltage to the fuel pump. Batteries fully charged and load tested? @Ozymandias just beat me to that. Check for any wiring issues along the way also.

I was wondering about that as the system does continually check for proper condition all the way to the pump itself, there can be several reasons why the circuit is shut down on purpose from the PCM.

 

[GeorgeLa]

Yes, I did change the relay. Put a new one in. Testing continuity between theTIPM relay input socket to the connector pin for the PCM, I get 0 ohms resistance. So no problem in the wiring from TIPM relay input to PCM output. When I read the voltage at that same socket (input from PCM to relay trigger pin) I get .8-.9 volts, not enough to actuate the relay. Batteries are fully charged. Not load tested but will crank the engine perfectly.

Who do you recommend to test/rebuild my TIPM? Who to you recommend to test my PCM?

 

[Ozymandias]

Did you measure that 0.8-0.9V with the relay in place?

 

[Topzide]

https://circuitboardmedics.com/ram-tipm-repairs

https://goecm.com/products/2003-2005-dodge-ram-2500-tipm-05026036

 

[GeorgeLa]

Did you measure that 0.8-0.9V with the relay in place?

No, I measured it with the relay taken out and probing the socket in the TIPM that is the output from the PCM.

 

[GeorgeLa]

https://circuitboardmedics.com/ram-tipm-repairs

https://goecm.com/products/2003-2005-dodge-ram-2500-tipm-05026036

Thank you!!!

 

[Ozymandias]

No, I measured it with the relay taken out and probing the socket in the TIPM that is the output from the PCM.

Very likely that's not working, this way you only get the pulses from the PCM that checks the circuit.
The PCM only sends power if he sees a working circuit.
Headlight are the same, no bulb, no power is sent to the circuit.

Take two strands of 18AWG wire pushed in with the relay 85/86 to measure what's going on with the circuit then.
And also it is possible that the PCM measures how much current the fuel pump itself pulls from the grid - and shuts down if to much is consumed (pump on its way out).
You can measure that with an AMP clamp, using a jumper instead of the relay.

And just to make sure, the relay you used is a 1:1 replacement, same property's like the one you have taken out - same, not similar.
For example if the factory is without a diode, and you used one with a diode, the PCM can't "see" the relay and therefor acts like it isn't there at all.

Especially in your case where a rebuild company already said that your PCM is fine you need to investigate EVERY other possibility first. And on modern days car there is way more to the electronic systems that we can imagine in our wildest dreams.

 

[GeorgeLa]

Very likely that's not working, this way you only get the pulses from the PCM that checks the circuit.
The PCM only sends power if he sees a working circuit.
Headlight are the same, no bulb, no power is sent to the circuit.

Take two strands of 18AWG wire pushed in with the relay 85/86 to measure what's going on with the circuit then.
And also it is possible that the PCM measures how much current the fuel pump itself pulls from the grid - and shuts down if to much is consumed (pump on its way out).
You can measure that with an AMP clamp, using a jumper instead of the relay.

And just to make sure, the relay you used is a 1:1 replacement, same property's like the one you have taken out - same, not similar.
For example if the factory is without a diode, and you used one with a diode, the PCM can't "see" the relay and therefor acts like it isn't there at all.

Especially in your case where a rebuild company already said that your PCM is fine you need to investigate EVERY other possibility first. And on modern days car there is way more to the electronic systems that we can imagine in our wildest dreams.

Thanks!

 

[Ozymandias]

When I google your code everybody says lift pump is bad, pulling to much current.
How did you come up with its the ECM?

 

[GeorgeLa]

When I google your code everybody says lift pump is bad, pulling to much current.
How did you come up with its the ECM?

I bought the truck new. It has 52K miles on it.

This started with A/C not working. Took it to a local repair shop about 4 years ago. They hooked up their Snap On Solus and said “dash controller is bad or PCM is bad, can’t tell for sure”. I replaced dash controller. Still no A/C. I pulled the PCM and sent it out for repair. I was told “we can reset it but there’s a high probability it will have a problem again so we recommend a rebuild”. I opted for the rebuild. Got it back, installed it and it started and ran for about 20 seconds. I read the codes and it had P0628 and a couple others. I sent it back. It was returned and I still had P0628 and a couple more. I got disgusted and moved on to other projects.

I got back to it recently. Read the codes and have P0628, P2122 and P2128. I sent it out to another PCM repair place and the just reflashed it, didn’t open it up and said it was good. I put it back in and still had the three codes. They said send it back. I did and they returned it, didn’t open it up and told me whatever is causing the codes isn’t fixed.
I haven’t investigated P2122 or P2128 yet. I figured I’d start with P0628 first.

I can run the lift pump by removing the relay and removing the relay and applying 12V by jumping an 18 ga wire from the battery to the socket in the TIPM for the fuel pump relay. I would think if the fuel pump were pulling too much current it would blow the fuse since I ran it for several 30 sec intervals.

I’m leaning towards the PCM as the problem because I didn’t have these codes before I initially sent the PCM out for repair because of the A/C problem. In fact, before I sent the PCM out initially I had no codes.

 

[Topzide]

The other codes relate to the accelerator pedal and other fuel issues. This could be why the pump won't run. I would focus on the other codes first, since you've confirmed that the pump does run. With the way that the network is in our trucks, fix one line of code and then move to the next. Fuel pump would be the last line of code to fix. Codes are held in eproms, they may have been there right before you pulled the PCM and sent it out. A reflash may or may not have cleared them from the memory of the chip. Do you have a FSM, or just reading codes and throwing parts at it? There would be steps to follow in which code to work first. From the outside, looking in, I'd start with P2122 & P2128 now that you have confirmed pump runs. I would jump the pump and confirm amp draw with meter. Good luck.

 

[GeorgeLa]

The other codes relate to the accelerator pedal and other fuel issues. This could be why the pump won't run. I would focus on the other codes first, since you've confirmed that the pump does run. With the way that the network is in our trucks, fix one line of code and then move to the next. Fuel pump would be the last line of code to fix. Codes are held in eproms, they may have been there right before you pulled the PCM and sent it out. A reflash may or may not have cleared them from the memory of the chip. Do you have a FSM, or just reading codes and throwing parts at it? There would be steps to follow in which code to work first. From the outside, looking in, I'd start with P2122 & P2128 now that you have confirmed pump runs. I would jump the pump and confirm amp draw with meter. Good luck.

Thank you! After some of the input from this thread I realized it’s possible that the PCM might be shutting down the fuel pump because of the APPS codes for both APPS signals.

No, I’m not jut reading codes and replacing parts. Yes, I can clear the codes with my scan tool. In fact, when I got the PCM back the first time from the second vendor, I had about 10 DCTs upon install of the PCM. I cleared them, but the three I’m having trouble with remained.

Good advice on which order to investigate my problems. Thanks!