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P0400 due to Faulty ECM?

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4 years 8 months ago #31769 by jreardon
Replied by jreardon on topic P0400 due to Faulty ECM?


You wrote previously:

So, while the engine is idling, I disconnected the EGR plug and using test light connected at positive battery, I got Terminal # 9 lit up green and the 10,18, and 19 only dimly lit.

and now in the video you have terminal #18 with no light anymore. Is this because you had the engine idling as opposed to cycling the key on and off? Reproduce this to confirm.

( To anyone else following along terminal 18 is the ecm connector. In the video when Genes1s says 3, that's at the egr connector. It's the same wire. )

My thinking is leading me toward heat being an issue here. Can you get the car nice and hot and check the resistance of the circuit. You have a very nice setup there with the EGR connector backprobed light that. I'm thinking if can hook up the DVOM to the correct load side of the relay, you can do a resistance check with the EGR valve hot.

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4 years 8 months ago - 4 years 8 months ago #31797 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
So as far as # 3/#18 terminal, it is all flat lined both at cycles and idles.

Here is the summary. The steps are in sequence. Engine cold, IGN on, Engine Start, Idle, Revs, Engine off, Ign/on/off, key removed. See video also.





I would need to isolate the harness from the ECM and EGR to confirm short to ground at harness or ECM, or open EGR coil. When I tested the EGR resistance, it is too spec (at cold).

Perhaps you're on to something about the heat. I really wish I have 4 ch scope, I can just run wires inside the car and have it live.
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Last edit: 4 years 8 months ago by Genes1s.

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4 years 8 months ago - 4 years 8 months ago #31799 by jreardon
Replied by jreardon on topic P0400 due to Faulty ECM?
Okay this makes sense now. It's obvious the driver in the ECM is bad (no ground provided by driver). What killed it though? I think testing resistance of EGR when it's hot is only way to confirm. Or swap #3 control wire with a working control wire (harness circumcision required) or re-pinning at the harness connector, to see if good driver gets cooked. It's also clear the EGR coil is open since you're not reading battery voltage at the control wire.

Edit : The resistance test I illustrated is unnecessary if you don't have battery voltage on the control wire with a driver that's off (no ground).
Last edit: 4 years 8 months ago by jreardon.

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4 years 8 months ago - 4 years 8 months ago #31801 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?

jreardon wrote: Okay this makes sense now. It's obvious the driver in the ECM is bad (no ground provided by driver). What killed it though? I think testing resistance of EGR when it's hot is only way to confirm. Or swap #3 control wire with a working control wire (harness circumcision required) or re-pinning at the harness connector, to see if good driver gets cooked. It's also clear the EGR coil is open since you're not reading battery voltage at the control wire.

Edit : The resistance test I illustrated is unnecessary if you don't have battery voltage on the control wire with a driver that's off (no ground).


So, would the latest video proof that Terminal # 3 was not shorted to ground and leave us with the possibility that the root cause is the driver malfunctioning and not open control wire nor open coil?

I can confirm these again but there is no open coil condition since the EGR unit was working fine when plugged in the IACV connector ( I could see the shaft/solenoid movement at start up) and the resistance is within spec. Also I had disconnected the EGR hardness from the EGR and ECM and the harness has no short to ground and no open. I checked short to ground using test light. I checked open circuit using DVOM connectivity function.

Still if the driver is malfunctioning on that terminal # 3, what caused it and how to make sure that a new driver would not do the same way.

Perhaps, if the heat affect the resistant, like you say, it could affect the driver respond?
Last edit: 4 years 8 months ago by Genes1s.

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4 years 8 months ago #31805 by jreardon
Replied by jreardon on topic P0400 due to Faulty ECM?
I'm not sure how the shop tested the EGR valve. Did their diagnosis include usage of a scope?
Or did they command it open 100% on the scan tool sitting behind the wheel, noticed the car didn't stall, and then made the call the EGR passages were clogged?

The command to move the pintle was there but the damaged driver can't ground the wire, hence it couldn't move the pintle fully, therefore it couldn't stall the engine. Without this detail you can conclude (incorrectly) the EGR passages are clogged.

Assuming you have good contact on the #3 control wire, one thing is absolutely certain from your videos, #3 control wire does not get grounded because your light never lights on that wire. I am assuming this is an abnormal condition because the other control wires do get grounded. If the control wire doesn't get grounded it must have battery voltage on it. In your videos your multi-meter showed 0 volts on that wire. That means the #3 coil inside the EGR valve is open.

I believe what happened is the coil got shorted first, cooked the driver, and now the coil is open but only opens when it gets hot. That's the only way I can explain why it's working in the IACV harness. Mr. Danner says in his videos on ohm testing, something like, "if it ohms good it can still be bad, if it ohms bad, then it's bad." It's the only way I can reconcile those two facts. It's either that, or that control wire got shorted to power somehow. The driver doesn't die for no reason.

I would check for driver functionality backprobing at the PCM, just to double check. Redo the tests you did at the EGR valve but focus on just that one wire at the PCM since we know the problem is there.

Still if the driver is malfunctioning on that terminal # 3, what caused it and how to make sure that a new driver would not do the same way. Perhaps, if the heat affect the resistant, like you say, it could affect the driver respond?

The driver is inside the PCM so the computer is bad. What made it go bad? The EGR valve coil resistance went to 0, which sent unrestricted current to the driver when the driver provided a ground. On the topic of unrestricted current, did you have any blown fuses in the past on this car around the time you had EGR codes?

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4 years 8 months ago #31811 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?

Monde wrote: How about erasing the code and redoing the test? (#3)?


I erased the code when I did this test. The code will come back between 70-90 miles.

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4 years 8 months ago #31813 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?

I'm not sure how the shop tested the EGR valve. Did their diagnosis include usage of a scope?
Or did they command it open 100% on the scan tool sitting behind the wheel, noticed the car didn't stall, and then made the call the EGR passages were clogged?


They used the scanner to command the EGR to determine that the passages are clogged. I mentioned the passages were cleared 3 days before but they insisted that I need to clear it again B) . I asked how to check if the ECM is functioning properly and they gave me weird look so I left.

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4 years 8 months ago #32003 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
Update:

It has been 160 miles since I reset the CEL and did that testing. The CEL has not been on since then and when I did the same test on #3, I got signals just like the # 6. It was flickering at start up and revs and off at idles and on/off cycles.

This is super weird. I didn’t do anything else other than adding those jumper wires and resetting the CEL. Usually the CEL came back on after 80-90 miles, but this is almost double the miles and it hasn’t came back and I got signals on a terminal that was flat lined before...

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4 years 7 months ago - 4 years 7 months ago #32278 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
So it’s been 500 miles now with no CEL P0400. I’m tempted to remove those jumper wire and see if the problem comes back. How does this make any sense? Heat and resistant? Longer wire less resistant created by the heat.

It’s weird...
Last edit: 4 years 7 months ago by Genes1s.

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4 years 7 months ago #32528 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
Sorry I didn't jump it. All I did was splicing the wires to the EGR selenoid so I can have easy access to back probe them using test light. Ever since then, I didn't have any CEL anymore, its 600 Miles now.

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4 years 7 months ago #32562 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
I’m 100% positive that all passages and EGR Valve were cleared. I cleaned it last November and last month when troubleshooting the code. I’m going to remove to back probe wire and see if the code comes back.

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3 years 7 months ago - 3 years 7 months ago #42602 by Genes1s
Replied by Genes1s on topic P0400 due to Faulty ECM?
OK, this thing is coming back again. I bought a new Nissan brand EGR to compare and it still didn't work. Re-checked all sequences for troubleshooting steps and still coming with nothing.

When I compared the resistamce value between new and old, they were all identical and to spec. So, pretty sure old EGR is all good.




How do I energize the stepper? I have computer power supply that I can use to supply 12 and 5 volt. Doing in the car with ignition on and off doesn't do anything unlike the IACV motor which I can tell it cycles during ignition on.

Could it be EGR temp circuit? perhaps that is the next step.

I've been driving like this in limp mode for about 500 miles...
Last edit: 3 years 7 months ago by Genes1s.

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