I have a 2000 A4 coupe in my shop for the last month with a real head scratcher.

No Codes set
After brought to operating temp the car will simply shut down. Not all the time but once it starts doing it, it does it a lot. I've driven the car home (12 miles each way) several times without issue but this AM just as I turned the corner to my shop, it started it again.
Sometimes just turning the key on to start position & the car will fire back up.
Sometimes it just turns over with a no start.
Then if you shut the key off & wait 10 seconds or so (not that the pull key message is popping up or anything.) and it will start.

This car DOES have the GM column lock harness under the drivers knee bolster. Column lock appears to function fine but I think the lock plate is removed as well as wheel never locks

Fuel pressure/pump ARE working 56-58 psi still showing when it dies
Today I did notice that the pump continued to run after engine died (not just the 10 seconds after, but much longer) and the regulator was knocking? Maybe there is aeration going on? This isn't every time, just a couple times it did this.

All the usual suspects have been addressed:

All chassis ground points cleaned (under hood, engine block, A pillar, rear frame)
Ignition switch cleaned/rebuilt & a replacement tried.
PCM removed & wiring harness & ends checked for obvious damage, removed the plastic wrap & inspected individual wires the first foot.

Swapped the fuel pump fuse w/ reverse lights (same fuse part number).

BCM connections & wiring (including star connectors) checked....

Again, no PCM, BCM or TCS codes are being set when this happens?!?

Open to suggestions on next thing to check??

 

Are you using the dic to pull the codes? No codes would seem to point to the ignition switch but I have no experience with this.

 

I have a tech II, no codes set other than if you try to start without dropping back to Neutral/park if it dies on the road and occasional communications errors with the RFA, which is why I cleaned the star connectors. I've had the tech II plugged in monitoring the engine data display when this happens & it also stays lit. A partial indication that ignition switch is still supplying most power.

Update on CLB. The factory one was NOT plugged in, the relay was bad, I replaced it with a known working one & plugged it back in to provide a positive response on the green wire. No post test time yet. As an aside, the factory CLB relay if white is a total POS. I took it apart & the damn thing has a micro relay inside the large relay case, no wonder it fails so quickly.

 

First and foremost,,,,,,, GET RID of the factory crap column lock harness and install a LMC5 unit..

Second, Please examine the door/s function when the car dies. See if you have all functionality on BOTH door locks and window operation.
The door power connector is WELL KNOWN for having **** poor electrical connections because the female pins spread apart and cause the module to rapidly loose power and regain power thus corrupting the serial data lines. Look for damaged female pins in the door connectors

You normally see lots of no comms and U series codes when this happens. PLEASE use the DIC DTC reading function the next time the car DIES. When the car dies, DO NOT CHANGE anything and do not turn the ignition off and then back on!! Pull up the DTCs as soon as the engine shuts off!!. Post everything that you see including NO COMMS, U series DTCs and codes in modules that have nothing to do with the problem. They are all clues

Third: I’ve see the IGNITION RELAY #42 in the under hood fuse box fail.

If you can get the car to fail in the shop, find the MAJOR module fuses that are supplied by the HOT in RUN & START power and see if you have full battery voltage at the test points on top of the fuses..

If you truly have an issue that causes the engine to shut down without leaving DTCs, the PCM thinks that you are turning it off with the key.

FOURTH: Unplug the two electrical connections for the IGNITION SWITCH. Carefully examine the FEMALE PINS and make sure that they are not deformed and spread apart and not making good contact with the male pins on the switch. I’ve see some that were so loose that the female pin was burnt and melted in the connector. Same for the power pin in the Steering Wheel Multifunction Switch female connector when you have a headlight control issue. 

BC

 

Bill,

Interesting stuff going on now... I pulled drivers door control connector & tightened up all the power connectors, fired it up & after warming it shut down. Now I'm getting major U1016 PCM communication loss with most of the subsystems when it shuts down. I thought I would check the wiring from the star connector to the last connector before it goes down to the PCM, which from the diagrams should be C150, down behind the battery. I've found it and planned to unhook it & Star 1 in order test for a break or short to ground. Next would be to pull the connector from the PCM & test back to C150. However, I'm not finding C102 which by the manual should be close by C150??

Now for the real kicker!! I pull the underhood fuse panel loose to look at how the harness runs under it & found this!!! A jumper that had been added by someone & is now come loose... It jumps between E8 on the light grey connector, circuit 641 which I have yet to identify other than Ignition 3 and appeared to have connected to A1 on the black connector, circuit 839, which I have identified as fuel injector 8 power supply. I wondering if they vampire connectors they used are cutting too deep into the wires or if they had resolved something else by using a jumper?? I hate when people jury rig things instead of fixing the real problem.

 

Trog..
The seat electrical connector is another connector that can cause communications issues.

Good find on the butchered wires. Get that straightened, check the seat connector plug out and see where you are at after that.

Bill

 

I would suspect you are looking at a failure in the injector power circuit and that hack job was to get power to the injectors. Possibly relay 42 like Bill posted.

As for the comms issues. I would suggest you pull the star connectors and jumper only the BCM and PCM back together. See if it will run OK and then start adding circuits back in until you find the problem one.

 

We will be watching!

 

Ok... after many hours of removing door panels, seats, RFA, door seal (accordian) & the ignition switch connectors again as well... all connectors taken apart & tightened. Also repaired the cuts in the underhood fuse wires. And installed the LMC5 recommended by Bill.

We still have the same shut down issue... car gets up to full temp & just randomly shuts off. Turn key off, back on, fuel pump primes, rail still shows pressure, engine turns over but no start. All we fixed was we now have no communication codes being set... It just shut down & there are NO/ZIP/NADA codes set. This is REALLY getting frustrating? After a few key off/on she fires back up but dies again in a few min.

Next I will need to see if we get power to the coils & injectors when this happens... something is cutting out.... Oh, I have tried swapping the primary & fuel pump relays with some spares I had laying around.... no change. Somewhere a relay or circuit is heating up & breaking a connection...

underhood major fuses still all had power, I need to check major dash fuses tomorrow.

 

Wow, bugger. Yup, look for lost power or lost fuel pressure to begin. Since you seem to be saying it just cuts out I'd think power is being lost to something important.

 

ttt

 

If you can figure out if you lose SPARK or FUEL it will get us to a finer trouble spot.

When the engine dies, press the drivers fuel schrader valve and see if you have pressurized fuel at the fuel rail..

BC

 

I've had a fuel pressure gauge hooked up for a week. always shows 50 to 58 psi....

That being said, I was just reading another post (towards todays top) about a no start/dying issue (sounded like fuel pump) that sounds similar. Can the pump show pressure of just air?? I DO know that the jet pump is working as I've been monitoring a bunch of cars lately to help see how the left/right sending units respond after a start up. Seems most tanks settle/equalize overnight & then within 5 min of running the right tank goes down to almost empty & the left gets filled. INCLUDING on this car. Has about 5/8 of a tank & before first start of the day (mid voltage on both sending units). After a few min the sending units show movement & a correct balance of low voltage right, full voltage left happens within 4-5 min.

 

Update!! So... cleared everything again today & removed my fuel pressure gage (I need to install a pressure relief valve in my line) so I could check the rail manually.... when it shuts down... the fuel rail has pressure but is just AIR pressure.... just a few dribbles & then nothing... pump runs, only another dribble. The fuel filter was changed last month so looks like it might have been the damn pump this whole time! Either the inlet is plugged or?? The car runs for a bit & then the pump stops sending fuel... guess I can check at the filter first & see if the pump sends fuel to there.

 

Time to pull that pump assy out for for a look see..

Bill

 

Borrowed a better fuel test gauge than mine (which doesn't have a drain)... After checking for fuel flow right at the pump (which was good). I now seem to have fuel all the time at the rail, however when I drain (while running) I get a lot of air (clear hose for drain off) I would think there should be NO air in the fuel line? I think this was the connection at the rail, the rubber gasket in the fuel gauge was blocking flow, I cut it back a little & buffed it flat, seals now, no air bubbles, good flow from the drain & gauge still shows 10psi w/ full fuel flow to my gas jugs.

I'm going to try a GM brand filter (which has built in regulator for this year). I have a WIX on there now (almost new) so going to be pissed if that is the issue??

I've gone ahead & drained the tank & pulled the pump now as well. Strainer is a bit gunky (inside) appears to be rust type residue near the pickup plastic outlet. You can't of course really get at it. Blew w/ air hose the brown gas gunk is light but I think at this point I should just replace the damn thing.

 

If that filter doesn't have a regulator, well....
No codes for low pressure.

 

2001 Z06 - I've had a similar problem where the engine would quit unexpectedly without codes and re-start later on, although not quite as predictable as yours. Thought I had it fixed after doing the Bill Curlee Ignition Switch Rebuild, but no such luck. To make a long story short, I finally got a code immediately after the most recent shutdown at 70MPH: P0335C - Crankshaft Position Sensor. I need a starter anyhow so I'll replace the CPS at the same time. I've also replaced the fuel filter with a Wix.

 

BTW... when I drained the fuel tank I used the gauge bleed off to drain the last couple gallons while the engine was running. When it did run dry, this was NOT the immediate shut down like I am getting, it stumbles & stutters as the fuel pressure drops & air is in the lines...

Rethinking this I'm now wondering if it is fuel??

As for the CPS codes, we did have that a few times as well, but by the service manual, the code is ONLY set while trying to start the car. It would also set the trans gear switch code with also occurs when trying to start the car in something besides park/neutral. I chalked it up to trying to start the car while still moving... I even caught myself trying to do it one time when the car died on a test drive. You pull over & turn the key... then see the trans is still in drive.

 

If it is a sudden cut-out then I highly doubt it's a loss of fuel pressure. It's an electrical failure.