On The Road / Help With Error Code

[cerberusiam]

Might be the AC compressor connection causing the problem. Along with the fan, the AC activation wire can get scuffed on lines and such causing all manner of problems. Worth checking it.

 

[ReelDuel]

I'll check that tomorrow after work. Wingman Day at work tomorrow starts at 0730.

 

[PWong]

Why does the A/C compressor not work when it does this?

When the BUS is down there is no communication between the HVAC control module and ECM so ECM will not run the AC clutch.

 

[cerberusiam]

The BUS is not down, Smarty is communicating and pulling codes, truck is running so the BUS is up. The short is kicking garbage into the system and causing the problems, but, only on peripherals.

 

[Prairie Dog]

In digital circuits, there is more than one bus. Even more tothe point, individual address and data lines of a particular bus can be shorted (pulled down) leaving other lines functional.
If a short is puling one bus or address/data line down, another may or may not be effected. Hence the ability to report that another circuit is malfunctioning.
Every sensor wil have its own address line but will share data lines with other things.

 

[PWong]

Well if it is not totally functional and ECM says P1652 then it's partially down if not totally down at that moment. LOL

 

[PWong]

If the AC was not working then I would like to check D25 wire going to the HVAC control module or the control module first.

 

[ReelDuel]

I didnt drive the 04 today. Got home cranked it up and everything is working fine. No codes. It is 25 degrees warmer than current morning temps. So strange to have a solid tie to temperature outside. I'll test it again in the AM

 

[ReelDuel]

If the AC was not working then I would like to check D25 wire going to the HVAC control module or the control module first.

Where do I find the D25 wire" and HVAC control module. Sorry IDK much about this truck. Trying to get these problems fixed so I can sell it. Thanks everyone

 

[Prairie Dog]

Well if it is not totally functional and ECM says P1652 then it's partially down if not totally down at that moment. LOL

Not sure what the LOL is about but there's your proof of multiple busses. One can report that another has an issue.

 

[cerberusiam]

Not sure what the LOL is about but there's your proof of multiple busses. One can report that another has an issue.

No, it is reporting THE bus has a short to ground. There is one J1850 PCI communication bus, everything is on it, fan, AC, crank sensor, cam sensor, ABS, cluster controller, OBD port, etc. If the J1850 goes down Smarty says NO BUS, the dash says NO BUS, and quite frequently the engine does NOT run and drive. Smarty is connecting and reading the codes so the J1850 is up but the ECM is detecting an anomalous reading somewhere in the system, it is not so severe that ECM is shutting down communications, there is just garbage on the bus that is being read as a potetial short.

This could be a bad fan, could be a scuffed wire in the harness, could be the OBD port, could be the cluster shorted internally, could be the ECU failed internally. Being temp related and a jarring fixes it there is a better than average chance the gauge cluster is the source of the problem since it is showing the errors. You have to run thru the diagnostics to see what is happening. Below is the diagnostic test, basically check the D25 circuit for resistance between the battery negative, if it is low start checking ALL the other circuits on the connector for high resistance which indicates a bad node on the bus. Again, not OTHER buses but other LEGS on the J1850 comm bus.

Diagnostic Test
1. ECM
Turn the ignition off.
Disconnect the ECM harness connectors.
NOTE: Check connectors - Clean/repair as ecessary.
Measure the resistance between the (D25) J1850 circuit in the ECM harness connector and battery negative.
Is the resistance less than 10 Ohms?
Yes >> Go To 2
No >> Replace the ECM.

2. (D25) J1850 SHORTED
Measure the resistance between the (D25) J1850 circuit and all other circuits in both ECM connectors.
Is the resistance greater than 100k ohms?
Yes >> Refer to the Body Diagnostic book Communications section.
No >> Repair (D25) J1850 shorted to another circuit.

 

[Prairie Dog]

Actually Cerb, your first paragraph verifies what I wrote. But it appears my attempts to impart some knowledge of digital electronics (my expertise) is just stepping on toes.
So I'll not comment further
Best of luck to the OP. Trully hope your fix is cheap and simple.

Scott

 

[cerberusiam]

Actually Cerb, your first paragraph verifies what I wrote. But it appears my attempts to impart some knowledge of digital electronics (my expertise) is just stepping on toes.

On the contrary, it defines what is actually in the truck as verified by the FSM and diagnostic procedure. I hear what you are saying, I am saying it is incorrect because you are mixing the definitions of the network interface with the physical layer implementation.

SAE J1850 establishes the requirements for the network communication interface, that is the communication bus used by the system as whole. There are 2 common physical layer implementations for signaling on a J1850 network, PWM and VPW, and that is what you are trying to insert into the network layer definition. You can assert multiple buses but the truck does not care, it recognizes and reports on ONE SAE J1850 PCI communication bus for a variety or errors. Communication networks can in fact run with errors, they do all the time because there is a definition on how to handle them at the network level. There is no definition to handle errors at the physical layer because that is not a network level function, it is a physical layer implementation, and they are in a range or out with no partially up or down.

As demonstrated by the OP's description the comm bus can have errors and still function while certain components on the same bus are non-functional. The diagnostic procedure defines multiple scenarios for the P1652 error, in particular shorted to ground or shorted to another circuit. It is ONE bus, multiple signalling implementations and componenents. When bus circuit shorts to another circuit it generates noise that may effect multiple components because the signal is now corrupted BUT the ECU only sees the single error as a catch all. Shorted circuits will indicate where to start looking for the problem by components that are non-functional, a dead short to ground will shut the whole system down and NOTHING works. The ECU either went into protect mode or it burned out a critical component. Reference a short in the fan, a crossed wire on the OBD port.

Examples of short to other circuits are cluster, ABS, etc. A mildly scuffed wire on cam\crank sensors or AC control will emulate a short to circuit, you get a P1652 error but it is not really hard shorted to ground, the noise generated is causing the error and malfunction.

This is just standard automotive network diagnostic procedures as defined by the FSM and general practice, you can call it what you like but it doesn't change the WHAT and HOW in a pre-2006 Dodge truck.