I don't want to be a parts changer
Hello everyone. I have a problem car that I thought would be straight forward but it's kicking my butt right now. It's a used car lot car (go figure) and the A/C clutch does not engage with the switch. The car lot tried a new HVAC control head and after much circuit testing, I replaced the ECM. The problem still exists and I don't want to change another part until I'm certain of success.
It seems to me the only things left are the tipm or cluster but I would like to be able to prove out the diagnoses. I will list out the things I have tested and verified and see if anyone can give me some further direction.
- I have fully charged the system with .51kg of R134A
- The clutch will turn on with a scan tool
- Manually engaging the clutch with the engine running resulted in good A/C pressures and cold air from the vents
- There is battery volts out of the tipm to pin 11 at the PCM - If I ground that wire the clutch engages
- I tested the pressure switches by connecting a testlight from power to pin 10 at the ecm connector - It lights
- I see the proper switch inputs on the scanner when working the A/C controls in Cluster data
- ECM data only shows clutch on/off. It always read off no matter what.
- TIPM data does not respond to the HVAC switch changes, except when I command the clutch on through the tipm
- The A/C indicator light on the HVAC controller never comes on. If I ground pin 5 at the switch it lights. It also turns on with the scanner
- No codes
I have verified the clutch circuits, the tipm circuits, the HVAC control circuits. From the diagram I gather that the HVAC control inputs go to the cluster and the cluster sends the command for clutch turn on to the ECM over the Can Buss.
Viewing cluster data I see all the HVAC switch inputs. When in TIPM data I don't see the switch inputs, however, if I turn the clutch on from within the TIPM, I do see the clutch on/off pid change.
I guess what I want to know is if there is a way to test for the turn on signal being communicated from the cluster to the ECM? Or do I just change the most likely failure item? (tipm)
UPDATE: Here is the description and operation of the A/C clutch circuit.
"A/C clutch engagement is controlled by the Powertrain Control Module (PCM) or Engine Control Module (ECM), depending on engine application. When the A/C switch is pressed to the On position, the switch sends a request signal on a dedicated hard-wired circuit to the Cabin Compartment Node (CCN), which sends a message on the Controller Area Network (CAN) B Bus to the Totally Integrated Power Module (TIPM), which then transfers the request on the CAN C Bus to the PCM/ECM, which determines if operating conditions are correct for A/C clutch engagement. When all operating conditions have been met, the PCM/ECM sends a signal on a dedicated hard-wired circuit back to the TIPM to energize the internal A/C clutch high side driver. When energized, the A/C clutch high side driver provides battery current to the A/C clutch coil. Depending on engine application, a gateway module is used by the TIPM to communicate to the PCM on the CAN Bus.
The A/C clutch control system is diagnosed using a scan tool (Refer to 24 - Heating and Air Conditioning/Plumbing/COMPRESSOR, A/C - Diagnosis and Testing)."
Other than basic circuit checks there is not much more help in service info.
The other input is ect. What is the reading. It appears the the module is keeping the compressor off. The only thing I didn't read you mentioning is the ect PID
I watched it in OBD2 data and it is well within the normal range. It agrees with air temp after a cold soak.
It goes A/C control head to Cluster to TIPM to ECM, Then ECM confirms operation and grounds pin 11 to the TIPM. Is there an A/C request PID in either the cluster or TIPM?
See my notes and video above.
So by what you wrote, you have a request in the Cluster, but not the TIPM? So the message is being stopped in the cluster. If that’s the case try the “reset ecu” function for the cluster. i’ve Had luck with that before when they loose random functions. The Autel should have that function.
It does appear to be a logic problem since all the hardware works. I suspected the turn on message is not being forwarded by the cluster, I just had no way to prove it. I will try the reset function when I'm back at the shop.
Power steering switch ok ?
Good thought. No pid shown on two scanners. The wiring schematic shows a switch input at pin 30 of connector C3. There is no wire at that location and I don't see a switch on the car.
do you have access to CCN Cabin Compartment Note
the ccn send a message to the totally Integrated Power Module (TIPM) wish transfer the request to the PCM/ECM wish determine if operating condition are correct for A/C clutch engagement When all operating condition have meet the PCM/ECM send a signal to the TPIM to energize the internal A/C Clutch high side driver
Yeah that's pretty much the sequence of events, Either the cluster is not sending the message to the TIPM, or the TIPM is not relaying the message to the PCM. All that just to get some cold air.
I would not suspect the tipm because it is just a relay box and from your notes it seems OK. I know that this sounds like a "bubba fix" but at this point try a hard battery reboot just to clear the ecm ( after finding the proper procedure) it being an 06 maybe it has some error it cannot communicate. Like I said just a thought
The TIPM is like a gateway module. Powertrain control module is on CAN C, Cluster is on CAN B. check the communication lines if all is correct with the pressure switches and Coolant sensor. May have a problem with TIPM.
Is there an evaporator temp sensor on this car?
The A/C low pressure switch acts as one on this vehicle.
Before you replace anything what is the current part number of the HVAC control head? I deal with used car lots too. Before I do anything I verify they have installed the correct part. They are notorious for heading to the junk yard and assuming that if the part looks the same, it must work. I have been bit by that more times than I care to admit.
Yeah, I was thinking about that as well. Although it's not necessarily the problem here I would look at it. This sounds like a "round 2" kind of job. diag.net/msg/m1fz9kf411… Bad parts: Inspect any and all parts that have been replaced on the vehicle, chances are very high the car had one problem and the attempted repairs added a second problem. If control units have been…