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Dan
Dan, Technician
Category: Jeep
Satisfied Customers: 23739
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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P0685-AUTO SHUTDOWN RELAY CONTROL CIRCUIT P0688-AUTO

Customer Question

P0685-AUTO SHUTDOWN RELAY CONTROL CIRCUIT
P0688-AUTO SHUTDOWN RELAY SENSE CIRCUIT LOW
Submitted: 1 year ago.
Category: Jeep
Expert:  Dan replied 1 year ago.

Hello, my name I Dan. What all has been done so far to try and fix? Thanks

Customer: replied 1 year ago.
Hi Dan,Here is what is happening. It started a month ago, where I would start the vehicle and after anywhere from 1 second to a few minutes if the vehicle was at idle it would start to quickly drop in rpms and bounce back up over and over until the engine would stall. I can then restart the vehicle right away and the same thing will happen. If the vehicle is moving and rpm is above 2000 the vehicle will not stall and the rpm drop outs do not happen nearly as often. This started while I was traveling in Boston and I live 5 hours away in Philly. Since it seemed to drive ok with the rpms up above 2000 I drove the vehicle home. During the drive home there was one time when the low oil pressure light came on and the dash said there was 0 oil pressure, I figured there was an electrical problem and they could be related, plus I figured if oil pressure was really at 0 the engine would seize rather quickly. About 15 minutes later the oil pressure was reading correctly again, and I have not seen that issue again, I just wanted to mention it in case it's somehow related. I get two codes, P0685 and P0688, sometimes together, other times one by itself.Have all data account for the vehicle. Went through the steps for both P0685-AUTO SHUTDOWN RELAY CONTROL CIRCUIT and P0688-AUTO SHUTDOWN RELAY SENSE CIRCUIT LOW.When going through P0688-AUTO SHUTDOWN RELAY SENSE CIRCUIT LOW I can get all the way to the end, where it says to replace PCM. So I purchased a new PCM for this vehicle from the dealer and had then enter the vin number, the issue remained. I had sent the original PCM to someone who said they could replace the faulty capacitor, when they recieved the original pcm they said the capacitor was integrated into a pressed in chip and they could not repair it, but it was defective.I have also put in a new ignition switch as well as a new crank position sensor.Going back to the P0685-AUTO SHUTDOWN RELAY CONTROL CIRCUIT, when I get to step 5. (K342) ASD RELAY CONTROL CIRCUIT SHORTED TO GROUND I hit a wall. It asks "Measure the resistance between ground and the (K342) ASD Relay Control circuit in the IPM (Pin 85). Is the resistance below 100 ohms?" I don't get a reading. I have the terminal rebuild pack for the PCM A, B, and C connectors so I made a new wire circuit for pcm connector 3, pin 3 and ran it to pin 85 on the ASD relay. Tested resistance again on the new circuit and nada. Started the vehicle and still have the same issue. I then probed the "K342" circuit that I made and saw it was 12v with the vehicle off. When started it drops to 6-7 volts, and that's where I left off for the night.
Expert:  Dan replied 1 year ago.
I'd just run new wire from relay to pcm and see if that helps, you have replaced everything other then the wire it sounds like. If that doesn't help and relay/connections are good then the new PCM is the problem. Let me know how it goes or if you have more questions, thanks.
Customer: replied 1 year ago.
I did run a new wire from pin 85 on the ASD relay all the way to connector 3, pin 3 on the PCM connector. Should I be seeing a constant 12v under normal operating conditions on that circuit? If so, to rule the new PCM as being the issue, can I take the connector 3, pin 3 on the PCM connector and put it to a good 12v and try operating the vehicle? Wouldn't that take the new and old PCM out of the equation?
Expert:  Dan replied 1 year ago.

You should be seeing 12v when circuit is not grounded, if your seeing less then 12v that means there is a wiring problem. When PCM grounds brown/white wire voltage on control side of relay will drop to 0. If you ran new wire then monitor voltage at pin 86 during problem, if it drops below 11v you know there is a wiring/connection problem between relay and fuse. If good then monitor ground on pin 85.

Expert:  Dan replied 1 year ago.

Does code set instantly if reset?

Customer: replied 1 year ago.
Ok, with the vehicle off I see 12 volt on the brown/white wire with the relay installed. As soon as I start the vehicle the voltage on the brown/white wire drops to 6-7 volts. As the rpms start to drop and rebound I can see the voltage go from 6-7 with the engine running and then spike up to 10-12 volts as the rpms drop and rebound, until the vehicle dies. I don't believe voltage drops on pin 86 during the rpm drops and rebounds, but will double check in the morning.The code(s) do not set instantly. I can clear them and then it usually takes a few cycles of the engine stalling out for them to come back, well at least to trip the mil light. I don't know if they are stilling there as pending or not, this scan tool wont say if they are pending.Is there anything else I should look at before reporting back about voltage drop on pin 86?
Expert:  Dan replied 1 year ago.

Monitor power on pin 86 and ground on 85, that will give us a little more clear idea of what is going on. I think that is best place to start. Keep me updated, thanks.

Customer: replied 1 year ago.
ok will do, thanks.
Expert:  Dan replied 1 year ago.

Sounds good, I'll talk to you then. Thanks.

Customer: replied 1 year ago.
Ok, started with pin 86. See 14v when the vehicle is running. When it starts to drop rpms/stall out the voltage never goes below 12.8 (Did it a few times).I then went to pin 85. Vehicle off I see 12v. As soon as the vehicles starts it drops down to .8 volts. When it starts to drop rpms/stall out I see quick voltage spikes, like it shoots up to 3 volts and then shoots back down to .8v if the vehicle does not stall out. When the vehicle does eventually stall out I see 12v again. This is the brown/white wire from PCM connector 3, pin number 3. This is the circuit that I installed a new female terminal in the harness for pin 3 (to verify it was making good contact with the male pin in the PCM) and ran a new wire to the relay, and spliced it at the relay pin, so it is still using the original relay pin connector for pin 85. With that being said can I assume I have another defective PCM? If so, is there a way to wire it to verify that is the cause? Like feed a ground back to the PCM on this circuit to keep the vehicle running and adding a ground for pin 85 (instead of it receiving it from the PCM)? If i'm jumping the gun let me know haha. Thanks again.
Expert:  Dan replied 1 year ago.

I'm not sure if backfeeding ground to PCM will allow vehicle to run, it is definitely worth a try. If anything you will know PCM is the problem if the relay stays engaged because right now it engages then disengages. Let me know how it goes or if you have more questions, thanks.

Customer: replied 1 year ago.
Ok, I'll try that this afternoon and let you know the outcome.
Expert:  Dan replied 1 year ago.

sounds good, thanks.

Customer: replied 1 year ago.
I tried it this afternoon, it didn't help at all. Is there anything else to try? I have to assume that if the pcm was really commanding the vehicle off due to a sensor issue (like if cps signal dropped out) there would be additional error codes, right? It's just so weird to purchase a "new" mopar pcm from the dealer and have it have the same issue as my other pcm. And of course the dealer is trying to avoid warranting the pcm. The truck has basically become a track only vehicle at this point, if push comes to shove I could just rewire the fused ASD relay outputs that go to the injectors, coil, and fuel pump.
Expert:  Dan replied 1 year ago.

With PCM backfeed ground did voltage at pin 86 still go up and down?

Customer: replied 1 year ago.
I didn't monitor it on pin 86, but I can in the morning. I did on pin 85, and it showed 0 volts the whole time (when connected to the pcm I was seeing .8 volts).
Expert:  Dan replied 1 year ago.

I meant to say 85, sorry about that. If voltage was steady on 85 with wire backfeed to ground this proves wiring is good leaving PCM as the only possible problem. Let me know how it goes, thanks.

Customer: replied 1 year ago.
It was steady at 0, but does it matter that I was sharing the ground, meaning I used the same ground point to backfeed the pcm as well as to trigger pin 85 on the relay?
Expert:  Dan replied 1 year ago.

I'd assuming you were feeding pin 85 ground by backfeeding pin 3 at pcm?

Customer: replied 1 year ago.
What I did is take a good chassis ground and attach 2 wires to it. I connected 1 wire to pin 3 on connector 3 at the pcm. The other wire was connected to pin 85 on the asd relay.
Expert:  Dan replied 1 year ago.

If you connect to pin 3 at PCM this should keep pin 85 grounded, if not you know it is a wiring problem. If so then you know PCM is the problem. Let me know how it goes or if you have more questions, thanks.

Customer: replied 1 year ago.
Pin 3 at the pcm connects directly to pin 85 on the asd relay to provide ground, correct? So if I only connect pin 3 to ground what do I connect pin 85 to on the asd to trigger the relay?
Expert:  Dan replied 1 year ago.

There is a wire that runs from pin 3 of PCM to pin 85 of relay so wiring only pin 3 to ground should be the same as running 85 to ground assuming the wiring is good. Let me know if you have more questions, thanks.

Customer: replied 1 year ago.
One more question. Why can I not complete step 5 below? When I try to measure it I get infinity.5. (K342) ASD RELAY CONTROL CIRCUIT SHORTED TO GROUNDMeasure the resistance between ground and the (K342) ASD Relay Control circuit in the IPM (Pin 85).Is the resistance below 100 ohms?YesRepair the short to ground in the (K342) ASD Relay Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. See: Verification Tests\Powertrain Verification Test
NoGo To 6
Expert:  Dan replied 1 year ago.
If resistance is infinity that means wire is not shorted to ground which would also point toward PCM failure. Let me know how it goes, thanks.
Customer: replied 1 year ago.
OK, at the dealer now. They got me a new pcm and had them flash the Vin again. Same problem as before. According to the part numbers on the moose box both pcm are new, not reman units. I'm going to have it towed back home.
Customer: replied 1 year ago.
Mopar box.
Expert:  Dan replied 1 year ago.

I'm not sure what else could be missing, from tests we did we proved wiring is good. I'll open question up to see if someone else has some ideas. Next option would be running new wires between PCM and relay.

Customer: replied 1 year ago.
OK. I did run the new ground from the pcm to the relay that supplies the ground.