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Discussion Starter · #1 ·
I have a 2001 Passat with 4-motion and a 2.8l V8 that I am trying to find the ECU power relay for. If you take a look at the attached image you can see that I only have 1 relay in the ECM box. Looking at my VW manual I see that there should be a second relay behind the 373 relay in the picture. I removed the ECM and looked down the wiring holes to see if the relay fell down the hole but I could not find anyting. It is not that the wire is relay is missing, but rather that there is no place to connect the relay to. Were else could the relay be located?

Are the numbers on the relays constant? i.e. if I look through the rest of the relays for a 30, 428 or 429 will this be the ECM power relay?



 

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Discussion Starter · #3 ·
Thanks for that feedback. The issue is I have a no start condition, no fuel when I turn the key. After some trouble shooting, I found that the problem is the ground terminal on the fuel pump relay control side is not grounding through the ECU. The key gives a signal to the fuel pump relay when I turn the key, however, as the relay is not being grounded through the ECU the relay does not close. I can pull codes from the ECU so I assume that it, or part of it, is working. I was looking for the ECU power relay as I was told this could be a possible solution.

If there is no ECU power relay does that mean the ECU is always on? What would be the best way to check that the ECU is getting the proper power?
 

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Scan and post all codes.

As this is NOT likely to be an ECM issue, I suggest you forget about the ECM and its power supply for now.

When the key is turned to the on position the ECM grounds the FP relay for about one second, only 3 times after a reset.
A reset occurs each time the engine is started.
Otherwise the FP relay is grounded only while the engine is seen to be turning.

Is it cranking normally ?

While cranking the engine: (With everything connected, including the fuses)
What is the voltage between ground and each side of fuse #28 ?
What is the voltage between ground and each side of fuse #29 ?
What is the voltage between ground and each side of fuse #34 ?

With the ignition on, what is the voltage between ground and each side of fuse #32 ?
With the ignition on, what is the voltage between ground and each side of fuse #7 ?
 

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Discussion Starter · #5 ·
Thanks for the feedback,

Checking the fuses, as suggested, fuses #28,29 and 34 are all 0 volts while fuses #32 and #7 are the nominal 12 volts. After reading the codes I got a P1850, from Ross-tech I see this is titled "Powertrain Data Bus: Missing Message from ECU". I will have to do some more reading, but if you have any comments please let me know.

Another item of interest may be the fact that my transmission was acting up before the car died. Sometimes when I started the car the transmission would go into safe mode, so I would have to keep restarting the car till the transmission would start in normal mode. This issue seemed to come and go with a related fuel pump issue.

Thanks,
Austin.
 

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I repeat!
Is it cranking normally ?

Did you do the following tests exactly as requested, while the engine was cranking ?

While cranking the engine: (With everything connected, including the fuses)
What is the voltage between ground and each side of fuse #28 ?
What is the voltage between ground and each side of fuse #29 ?
What is the voltage between ground and each side of fuse #34 ?


If these tests were done correctly it is likely you have a faulty ignition switch, FP Relay, or ESS.

With the ign on, and in start position is there 12 V on ign switch pin 15 ? (Black wire to FP relay)
After cranking continuously for 7 seconds, is there 12 V on any of fuses 28, 29, and 34 ?

Do a full scan with VCDS and post the codes.
 

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Discussion Starter · #7 ·
Yes, it is cranking normally.

Yes, I did the tests with the engine cranking.

The voltage is the same on both sides of the fuses, as expected for a non-blown fuse.

The power to the fuel pump relay is correct, I do not remember the pin numbers off the top of my head but I was able to verify it using the wiring diagram. Also, if I ground the ground side of the relay coil the fuel pump runs as expected.

Ruling out the Fuel pump relay, and the ignition switch (already replaced) I think the EES (engine speed sensor) seems like it might be a possibility. Is there a simple way to test this?

I will try and perform the extra tests you suggested this week.

Best,
Austin.
 

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A full scan should always be the first part of any diagnosis.
Note: A scan doesn't always detect a faulty ESS.


Thanks for the feedback,
Another item of interest may be the fact that my transmission was acting up before the car died. Sometimes when I started the car the transmission would go into safe mode, so I would have to keep restarting the car till the transmission would start in normal mode. This issue seemed to come and go with a related fuel pump issue.
This could be another indication of a faulty ESS.

You can test the ESS with a meter, but that test is not always reliable.

After cranking continuously for 7 seconds, is there 12 V on any of fuses 28, 29, and 34 ?
If you get 12 V in this test, you can be pretty sure you have a faulty ESS.
 

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Discussion Starter · #9 ·
Thanks everyone for the help. Sorry, I am just now responding.

The problem was the ECM in the car. A new one off eBay for $15 fixed the issue.

Oddly, Vagcom would not connect to my ECM. If I disconnected my battery terminals and shorted them together to reset the computer the car would start once and I could connect to the ECM but every time I shut off the engine the ECM would revert back to not working the TCU would put the transmission in safe mode.

Again, I just installed a new ECM and everything seems to be working just fine now.
 

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Good to see it is running!

.........
The power to the fuel pump relay is correct, I do not remember the pin numbers off the top of my head but I was able to verify it using the wiring diagram. Also, if I ground the ground side of the relay coil the fuel pump runs as expected......
As grounding that pin also grounds a pin on the ECM, it is likely that is what damaged your ECM.
 
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