Limp mode?

[AudiA401B5]

I have an 01 Audi a4 and used to boost at 10 psi Car is basically stock other than my intake and downpipe. Can't boost over 5 psi now. Did a boost leak test and found a hole in a check valve next to maf. Replaced that and leak test is good. Still not boosting over 5-7. Is it possible the check valve sent something into limp? I heard n75 could be a culprit. Just want to try stuff myself before turning the car over to a specialist and getting pooped on with a big bill.

[Seerlah]

Reset your ECU by unplugging your negative terminal on your battery for like 10 min (in some cases, taking your ECU out is necessary). Be sure to do a throttle body adaption by placing the key in the starting position with the doors closed for maybe 2-5 min (I don't know how long exactly, so just a guesstimation).

[AudiA401B5]

Okay. I will try that and get back to you. So you do think that boost leak could send the car into limp mode?

[AudiA401B5]

Okay. I will try that and get back to you. So you do think that boost leak could send the car into limp mode? And will unplugging battery reset stock radio to where I need a code?

[Seerlah]

You don't need the radio code for the 01. I'm currently having technical difficulties with my vehicle and going to reset the ECU in a couple min myself. And having a boost leak makes you run lean. Running lean is what makes the ECU limit boost via n75 valve.

[AudiA401B5]

Grrrr. Didn't fix. N75 or waste gate?

[Seerlah]

Remove the line going from your wastegate to n75 (remove the line on either unit) and go for a drive. If you can boost, then your n75 is the issue. Be sure to let off the throttle once you overboost. You just want to see if you can make boost.

[Kylgod253]

I wish I had a N75 simply for the fact that my AEB boost issues are always much more of a headache. I am STILL leaking and won't boost over ~4psi and it spikes to the high of ~4 right when she wants to hit the next gear, then drops to 0 all over again. *face-palm*

I am unplugging my damn ECU now tho. The battery thing didn't help. I checked and re-checked for leaks. Its either my DV or waste gate flapper thingy whichisfuckingimpossobletoreachtoadjust.

[r1ashad]

I'm going through a similar situation were my car is only boosting 3-4 psi when I should be boosting between 15-16 psi since I have a GIAC chipped on 93 oct. My car sat for two weeks while I was away and I drained my battery when leaving an interior light "on" and after I got my car jumped, my car has been in limp mode every since. I have had a bad fuel level sensor since I bought the car in 2009 stock with no CEL. My check CEL has on been on for the past few months with no driving issues. I knew I had an turbo exhaust turbine outlet gasket leak and bad ABS sensor cuz i damaged it replacing my wheel bearing a while back, so had not been surprised to have a CEL.
- I unplugged the positive battery terminal over night to attempt to reset the ecu, but no luck.
- No apparent boost leaks.
- I fixed the turbo exhaust turbine outlet gasket leak yesterday.
- I even unplugged the MAF before starting the car to see if it maybe a bad MAF. The car started and idled fine. However was still boosting the same under throttle.
- I have also left my ignition on for well over 10 mins to try to reset whatever that is suppose to reset. I believe the throttle body from what I have recently been reading. Still no luck.

I have been holding back from taking my car to dealership or buying http://www.ecstuning.com/Audi-B5_A4-Quattro-1.8T/Tools/Scan_Tools/ES9950/

Has anyone ever actually fixed a limp mode issue?

[r1ashad]

ECU Reset/ Limp mode fixed
I believe that when i previously attempted ECU reset that maybe I didnt do it correctly. I really think that my car placed itself in limp mode when m y engine stalled out because it didnt have enough battery voltage to keep the car l running correctly. Not sure whether it makes a different whether you disconnect the negative or positive battery terminal.
ECU Reset:
-I disconnected the negative battery terminal for10-20 mins
- Re-plugged the negative battery terminal
- Before starting the car i left the key turned in the ignition for 5-10 mins
eLae
When i started car the CEL was "off" and so was the limp mode!

[Seerlah]

ALWAYS remove the negative terminal. And if removing your ECU or unplugging it, be sure to ALWAYS remove the negative terminal first. If not, you have a strong possibility of frying your ECU. But really good to hear you fixed your issue.

[rlcordova]

My Car is a Audi A4 1999. I have to warn the car every morning in order to avoid the limp mode. Once the car increase the water temp to normal, the car runs with no problem. If I do not warm the car and change the shift handler to DRIVE, the transmission perform a hard shift. If I start using the car after that, the car get into the limp mode. I need to turn off the car to get out the limp mode. I just wait the car to warm up and the car runs with no problem. What is causing this behavior?

[audi18]

My 01 was doing the same thing and mine is caused by the voltage regualtor being pretty well shot
Does yours light up all the lights for gear selection on the dash?

[Steve Chicago]

Both above posters...

Get your car scanned for trouble codes. Post all the trouble code numbers along with a thorough description of symptoms.

ricordova, I bet you have MAF or lean codes.

audi18, lit up gear selection indicates the TCU is in limp mode. See if you can find someone with VCDS to scan your engine computer AND your transmission computer.

[Rmartin8246]

ECU Reset/ Limp mode fixed
I believe that when i previously attempted ECU reset that maybe I didnt do it correctly. I really think that my car placed itself in limp mode when m y engine stalled out because it didnt have enough battery voltage to keep the car l running correctly. Not sure whether it makes a different whether you disconnect the negative or positive battery terminal.
ECU Reset:
-I disconnected the negative battery terminal for10-20 mins


- Re-plugged the negative battery terminal
- Before starting the car i left the key turned in the ignition for 5-10 mins
eLae
When i started car the CEL was "off" and so was the limp mode!

Does this "limp mode" have anything to do with the neutral switch? Or is this a separate issue?

I pulled a P0706 code. Will disconnecting the battery clear this?

[neil1976]

Hello i have a question about my A4 B5, i also have a video of issue if it helps, can someone tell me whats going on, i changed coil pack and have changed throttle body but dont seem like thats the problem, when i remove the plug from throttle body it works fine, can someone help here is my number if anyone in my area 514-943-6345 text me before calling so i know


https://youtu.be/2rCKLDuhC5k

[neil1976]

To make it simple, my A4 B5 sounds like under water on idle, when pressd on gas it runs, i changed coil pack and throttle body and still the same so i tried pulling the plug off throttle body and it stop lagging but without plug i have no acceleration , no more then 20km/h
Please help i am freeming out lol

[Seerlah]

That plug is what controls your throttle body. You have no cable on the 01 model. It is all electric and requires that connector.

[tnapp]

I've been having a similar problem in my B6 recently. Try unplugging the MAF and see how it runs