A4 Going Into Limp Mode

[tjcatman]

Ok, have a 2003 A4 3.0 that I purchased used with 147,000 miles. In the last cupple of months I sent it into Limp mode twice while reving the motor to the yellow. Shut car off both times and it reset itself out of limp mode. Last week my daughter was driving the car at 30 mph and it again went into limp mode. Would not reset and I had the car towed to the audi dealer in Reno. They called me and told me the car showed multiple misfire codes and that they checked the coils and injection ports finding nothing wrong. Did a leak down test on the motor and found #5 cylinder had 55lbs compression and determined that there was an issue with the exhaust valve on the number 5 cylinder. Quoted me $6000 to fix the problem. I picked the car up and trailered it to my local audi mechanic. While loading and unloading the car I noticed it sounded fine. Yesterday my local mechanic called me and told me the motor sounded fine so he did a compression test and all cylinders had over 150-160 lbs. I had him take the car home then back to work with no issues. Any ideas. I already purchased a low mileage used 3.0 that I was going to have my local mechanic put in but am thinking that would just be a waste of money at this point. There must be some explination as to why the motor shut down and the audi shop gave me a bunch of BS when I told them the car was running fine. Any advise would be greatly appreciated. Thanks

[MikTip]

The Audi has whats called DTC codes...

In order to properly troubleshoot, those actual codes from the limp mode are needed.

Sounds like your mechanic does your Audi maintenance so... ask him the same question.

[old guy]

Limp mode is when the ECM prevents the turbocharged 1.8T motor from adding boost. You have a non-turbo motor so I don't believe limp mode applies. Can you give a better description of the problem? Does the motor just drop to idle and not respond to the gas pedal input? Your problem could be something as simple as a defective or out of adjustment brake pedal position switch. If the ECM thinks you are applying the brakes for an extended period of time it will automatically override the electronic gas pedal input and put the motor at idle. The gas pedal input will not return until the brake pedal position switch resets.

[zz2h33]

my 3.0 used to go into what i would call "limp mode," which feels like about 1/2 the amount of power. The CEL and ESP lights would remain on during this cycle. Found out it was due to a broken ECU cover not sealing properly, letting water get to the ECU.

[MikTip]

OP never mentioned CEL/ESP lights.....

[tjcatman]

Trying to get the DTC codes from my mechanic. As mentioned above the car looses all power to about 10% feels like the motor is comming apart and has just enough power to get it off of the road. The two times it happened to me I just shut it down and it went away when I restarted the car. My daughter tried this and it didn't reset. I was told it is classic limp mode.

Is the ECU and ECM the same thing? Will look at the cover if I can find it. Still trying to figure out why the Audi mechanic at the actual dealer would say one cylinder (#5) had 50 lbs compression when my mechanic tested it and said all ok and car is now running fine. I called the dealership and they asked me if my mechanic put the car in service mode before he checked compression. WTF isn't a motor a motor that would either have compression or no compression?

Old Guy I will check the brake pedal but the car is a manual so I'm not sure it would have a brake pedal position switch or not. Thanks for the input.

[imnuts]

Trying to get the DTC codes from my mechanic. As mentioned above the car looses all power to about 10% feels like the motor is comming apart and has just enough power to get it off of the road. The two times it happened to me I just shut it down and it went away when I restarted the car. My daughter tried this and it didn't reset. I was told it is classic limp mode.

Is the ECU and ECM the same thing? Will look at the cover if I can find it. Still trying to figure out why the Audi mechanic at the actual dealer would say one cylinder (#5) had 50 lbs compression when my mechanic tested it and said all ok and car is now running fine. I called the dealership and they asked me if my mechanic put the car in service mode before he checked compression. WTF isn't a motor a motor that would either have compression or no compression?

Old Guy I will check the brake pedal but the car is a manual so I'm not sure it would have a brake pedal position switch or not. Thanks for the input.

Sounds like your car is misfiring, not limp mode. If there is no compression on a cylinder, or partial compression, that could be the cause. I'd have the compression checked again, or see if they can pull the plugs and check the cylinders with a borescope to see if anything is wrong.

Also, you're going to have a brake pedal sensor if you have a brake pedal. Last I checked, they came on all B6s, so you should have one too.

[old guy]

ECM and ECU are describing the same thing (Engine Control Module/Engine Control Unit). Both manual and automatic transmission have the brake pedal position switch. It is a four pin switch. One signal activates the brake lights and the other signals the ECM of your intentions. From your last description I don't think it is coming from the brake position switch. When the ECM cuts the throttle from an extended brake pedal signal the motor goes to idle. It sounds like you are still getting enough throttle response to move the car with a rough running motor.

[tjcatman]

imnuts, I did have my local mechanic re-check all cylinders and all read 150-160 compression. That's why this is so confusing. The Audi mechanic said #5 was 50 lbs compression but car in now running fine and my local mechanic said compression is spot on so thinks this is an electrical issue. Old Guy, yes the car idels down, engine idels very rough but you can move the car.

[tjcatman]

Still working on getting the codes, my local mechanic is very busy.

[tjcatman]

Picked up the car last night. Running fine no miss and check engine light is off. Does have an airbag light on and was told it is the one above the driver's side door. Any way to check the plug and see if that is the issue? Not sure where the plug is. As for the other, if the car continues to run fine I'm going to take it back to the Audi dealer and tell them I want my money refunded for the false diognostics test they performed stating I had a bad cylinder head.

[tjcatman]

No other ideas on this?

[coowhip]

You won't get your money back from the dealer for the diag. That is usually non refundable especially now that you took it somewhere else. What are the codes? No one can help with the diagnostics unless they have DTC's along with symptoms.

[imnuts]

I'd try to get two compression tests. One after it sat for a while from being off. If the pressure readings are low, or one is low, put a little bit of oil in the low cylinder(s) and test again. Also, good luck getting anything back from the dealer for diagnostic work.

[tjcatman]

Dealer gave me my money back for the faulty test they ran. While driving the car this weekend it started to miss and the check engine light flashed 4 times, then went off and the car has been running perfect since. I think it is an intermittant electrical issue but not sure where to even start looking. Hope to get the car back to my mechanic this afternoon to see if the the check engine light flashing four times stored in the computer. If it did I will post the numbers to get ideas.

[CyberPMG]

I would first get a new set of ignition coils. They are a very well known source for misfire issues. If the scan shows wich cylinder, you could simply exchange ignition coils and see if the misfire follows the move or stays with the same cylinder. If it stays it could be a fault spark plug (cheap fix).

If that doesn't fix the issue, then it may be that the ignition wiring harness may have a cracked wire and need replacing. I know 034 Motorsport makes a repair kit for the 1.8T engine, but I don't know if they offer a similar kit for the 3.0 engine. If there's no repair kit available, you may have to replace the full wire harness. I'm sure tests could be done between each ignition coil plug to the ECU to make sure everything's OK, but it would be a time consuming test to find out.

These are just suggestions.

[imnuts]

I'd check the wiring for the coil packs to see if you have any broken insulation. Could be the source. Also, when was the last time the spark plugs were replaced? If it isn't a constant misfire, it likely isn't the coilpack going bad. Other sources could be a bad/blocked PCV system or a faulty injector.

[tjcatman]

Checked the wires last night actually and found a wire with the insulation damaged in the harness but it was going to the front cylinder on the right side not the #5 cylinder where I was told the problem lies. I'm thinking first thing to replace the plug and swap the coil as indicated above to see if the problem changes cylinders. I could see the wires inside of the insulation where it was damaged but it did not appear as though the wire itself was damaged. Don't regall what color the wire was but I will check next weeked and post. My daughter has the car this week so it will take me a few days to do this stuff. Hoping she can get it to the shop this afternoon to see if they can read the code though.

[tjcatman]

So the check engine light came on again this weekend. Took it to shop and codes are PO 300 Random missfire. PO 301 (cylinder 1) PO 305 (cylinder 5) and PO 302 (cylinder 2). I'm at a loss. Please help.

[coowhip]

You need to fix all of the wiring for the CP's. If one is frayed or bad then they all need inspected and most likely replaced.

[CyberPMG]

So the check engine light came on again this weekend. Took it to shop and codes are PO 300 Random missfire. PO 301 (cylinder 1) PO 305 (cylinder 5) and PO 302 (cylinder 2). I'm at a loss. Please help.

I'm going to assume the CP that you swapped was between cylinder 5 and cylinder 2. Since cylinder 2 never misfired before, that would indicate the CP is faulty and needs replaced.

Because the misfire still happens with cylinder 5, it could still mean a faulty CP. If you haven't changed them, now would be a good time since you need to replace at least one of them. You can also throw in a fresh set of spark plugs to ensure a clean spark.

[tjcatman]

Ok I will recheck and repair or replace the wires and change the plugs. I have forgotten to mention also that ocasionally the sensor for the driver side tail light indicates it is bad even if though the light is working. Wondering if this might indicate an electrical issue that could include the engine problems I am having. Also the ABS light is on and I can not get it to go off. The dealer told me it was most likely a bad connection under the seat or a faulty drivers side seat airbag. Cleaned the connections and happen to have a second airbag that I tried to plug in to see if the light would go out but it did not. Then my hometown mechanic checked it and said it isn't the seat airbag at all but it is the one located above the drivers side door. Any ideas on how to locate the witeing to that airbag? Thanks for your help Audi Forms

[CyberPMG]

ABS is not related to air bags. ABS is the braking system. If you're having a problem with the air bags, it would have "air bag" light up in the gauge cluster. For ABS, it could be a wheel speed sensor going bad (there's one on each wheel) or the ABS controller going bad. Find a shop that specialized in Audis (or at least German cars). They should do a proper scan to find out what codes are being thrown to determine what the problem is.

[N1tr0]

My Baby just went into limp mode.
Wife was driving it and it just shut off on her. I went over and jumped it but it just idles very low and dashboard is dark except for BREAK warning light flashing, CEL on and AIR BAG light. Also, when I tried to change gear, it SLAMS into gear very hard, both drive and reverse do this.
Waiting for the tow truck to bring her home.
Any ideas???
2004 A4 Quatro V6 3.0

[SJorge3442]

My Baby just went into limp mode.
Wife was driving it and it just shut off on her. I went over and jumped it but it just idles very low and dashboard is dark except for BREAK warning light flashing, CEL on and AIR BAG light. Also, when I tried to change gear, it SLAMS into gear very hard, both drive and reverse do this.
Waiting for the tow truck to bring her home.
Any ideas???
2004 A4 Quatro V6 3.0

Limp mode is not a thing for the 3.0. Generally limp mode is when a turbo engine has a vacuum leak that causes an underboost condition.

What you have sounds like a transmission issue. Are the PRND lights on the dash illuminated? You're gonna need vcds to properly scan the transmission for codes and errors.

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