PRNDS on solid - cranks over but won't start

[Bigglezworth]

Remember ECU's don't just Plug N Play. They need to be configured/coded to match the immobilizer requirements of the car they are going in to which would then mean they would need the same going back to who you borrow from...

[kruat]

Ya I'd have to look at the wiring diagram once I get back to work, but there is a main relay located near the ecu. If it is bad then power won't get to the ecu. I just don't remember at this time which one it is.

[mik15]

Remember ECU's don't just Plug N Play. They need to be configured/coded to match the immobilizer requirements of the car they are going in to which would then mean they would need the same going back to who you borrow from...

or if you have good soldering skills, open up both ECU's and switch the eprom's boards

[bbogert]

My soldering skills are 'ok', I wouldn't trust myself soldering on such a critical component w/such a small working area... I'm guessing the ECU relay is the black 219 just next to the ECU, but that is a total stab in the dark -- the 219 does appear to be working, relay engages when key is turned. If there is one under the steering wheel that any one knows of I'd like to check that one. Is there a wiring diagram posted any where for the ECU? Also need to check to see if the ECU is getting power, but not sure which pin(s) are + and -.

According to RossTech:

Possible Causes

Blown fuse for control module - all checked

Wiring Harness issue - need to check power to ECU. Other than that I'm at a loss-

Failed control module - not sure how to test this other than just swap with a known good one. If I understand correctly, the car should start if using an ECU that's not coded for my VIN, but would immediately shut down. That would be proof enough I think to show it is a failed ECU if it starts up even momentarily. Or if PRNDS were not all illuminated.

Possible Solutions

Inspect wiring and terminals for CAN BUS between control modules.
Special Notes

As per TSB 01-07-54, do not replace the ECM for this DTC. Please see TSB for complete details.


Given that this started out as a somewhat intermittent issue, I'm inclined to think either relay somewhere or loose wire.


Thanks again for the replies, I appreciate it.

[ben916]

Didn't Nene have some strange issue were it was something simple like the speed sensor?

Also, someone stated that they have seen some green corrosion on ECU pins, might be something else to look at...

[bbogert]

Update: I hauled the beast to my mechanic who has determined the ECU is gonezo. He bypassed the relays and confirmed power is getting to the ECU, but none of the other systems can talk with the ECU so apparently its dead. He says there's nothing more he can do, it has to get fixed by Audi because Audi is the only one that can program the ECU for my car. Is that true??

I'm looking for an ECU, if anyone has one I'm interested. I have an appointment with Audi next Thursday (soonest they could do!). New ECU is $1300.00 according to my mechanic. Should be back up and running soon.

Thx again for the advice, very much appreciated.

[lswing]

How much do you trust this mechanic?

There are a few threads on here about coding another ecu to your car (so your guy was close), maybe $150 at the dealer to have that done? Used ECU for ~$300?

Use the site:rs6.com to search using Google, or maybe others will chime in with the exact info.

[bbogert]

Hi all,
My RS6 is back online -- turned out to be a failed ECU. Started out intermittent as noted in original post, then just stopped working at all. PRNDS lit when key turned, and radiator fan kicked on full speed after about 10 seconds. Vagcom showed no communication with ECU. Hopefully this info helps someone with similar issue.

So, $1300 for a new ECU from Audi + 1 hour labor -- could have been worse I suppose.

I had sent the original ECU to a company called AES Modules in Florida to repair it, but they said they couldn't remove the chip for some reason and offered to sell me a new ECU from Audi for $1300, so I used that quote at the dealership to get it for that price and saved a couple hundred bucks. I got the car back and its running great, but I noticed the cruise control isn't working. Could that be a coding issue on the replacement ECU? They were unable to pull any info off the old unit.


Thanks again for the input through my 'crisis'!! :-) Bottom line, I'm back on the road

[dab]

I just had the same thing happen with mine, ecu came loose overnighted to apr they fixed for free and sent back.

[RS Sick]

I've got the dreaded APR loose chip symptoms. Had the weird crank no start issues after alternator install, all fuses including 200a/150a mains were good. Wasn't communicating with vagcom but somehow randomly fired up last night. Took the beast out for a ride and it just died while slowly accelerating, PRNDS and MIL lit up amongst others. Crank but no start again so pushed it off the road and did vagcom again, same issue as OP, fans come on ~10 seconds while running scan. P1850

BTW, the car died on me exactly once (when parked) right before alt replacement and I was noticing low voltage so rebuilt anyway. Any thing else I should check or just send ecu off to APR for fix?

[RS Sick]

Here's another picture, don't have laptop to paste full scan.

[bbogert]

I've got the dreaded APR loose chip symptoms. Had the weird crank no start issues after alternator install, all fuses including 200a/150a mains were good. Wasn't communicating with vagcom but somehow randomly fired up last night. Took the beast out for a ride and it just died while slowly accelerating, PRNDS and MIL lit up amongst others. Crank but no start again so pushed it off the road and did vagcom again, same issue as OP, fans come on ~10 seconds while running scan. P1850

BTW, the car died on me exactly once (when parked) right before alt replacement and I was noticing low voltage so rebuilt anyway. Any thing else I should check or just send ecu off to APR for fix?

Hey, I'm no expert thats for sure. But this does sound exactly like the issue I had > PRNDS flashing followed by the fan running full bore. Its worth noting in my case, the issue happened once then self corrected for a week or something. Then got bad quick over a few days. I was able to restart the first few times i got the PRNDS flashing by fiddling w/the key, checking fuses etc, but I really think it was dumb luck that the car did fire. I didn't have APR programming in the car when the issue occurred, but I did do an APR trial (for a month) like a year prior to the issue. If I recall the 3rd party I tried to get to fix the ECU (some company out in Florida) but told me they couldn't repair it because of how a chip had been replaced/soldered on the board > I'm not sure if that was an APR thing or not. I couldn't send it to APR because I had returned the product.

Sounds like in your case the new alternator may have fried a chip on the ECU? Or it could just be a strange coincidence. In my case, no changes were made directly prior to the issue.


Good luck!

[nubcake]

<...>new alternator may have fried a chip on the ECU?<...>

Highly unlikely.
No communication with VAG-COM and fans full-on are usually a good indication of something bad happening inside the ECU.

[RS Sick]

I had the alternator rebuilt because I noticed ~12 voltage while driving over a week or two. It died on me and did PRNDS (while parked) exactly once before I messed with alternator.

APR chip was indeed the culprit. They re-soldered and were able to reuse the ecu. Their chip technology really is inconvenient. Reinstalled and all has been well over the last week.

The positive outcome is downtime allowed for sportec vent mod, order of aces IV and quantum blue oil. Pulls like a freight train.