TTuner

The vehicle is a 2002 Audi TT Quattro with 6 speed manual transmission. The engine code is AMU, which is the 225hp 1.8L engine. The car currently has 79k miles and all appropriate maintenance has been kept up. I bought the car at 61k miles and Curry's Automotive in Chantilly, VA had just recently replaced the timing belt, water pump, serpentine belt, and few other miscellaneous parts. Engine related modifications include GIAC chip, Borla catback exhaust, Samco turbo inlet pipe, and Bailey's diverter valve.

I've had no issues with the car whatsoever since owning it. One night I parked in a parking lot to meet someone to test drive another car, and then when I got back in to leave, the TT would not start. It would crank over but never start.

Upon returning that weekend, I pulled all 4 coils and checked them for spark with a spark testing tool (adjustable screw to simulate the plug gap and a ground) and they all had spark. I went ahead and replaced all 4 spark plugs since I was in there, and verified spark using a second method with the spark plug attached the coil and grounded to the chassis, and again it had good spark.

My next thought was I might not be getting fuel due to a bad fuel pump relay or fuel pump. I pulled the rear seat and listened for fuel pump operation. It was tough to hear whether or not the pump was priming upon turning the ignition on, but I did test the fuel pump terminal with a voltmeter and the pump was seeing 10.5 volts during cranking. I did replace the fuel pump relay for ****s but it did not solve the issue. To verify fuel was getting to the rail, I removed the fuel rail inlet hose and placed it into an empty 2 liter bottle and cranked the motor over a few times. Plenty of fuel was flowing as a few cranks filled the 2 liter bottle up about an inch from the bottom.

Mechanically speaking, I'm getting fuel, spark, and the motor has good compression so the car should be firing up. My next inclination was to test things electrical as it seems to be related to an electrical problem (i.e. bad sensor that is engine start critical). I had no Check Engine Lights, and even used a generic OBD-II scan tool to verify there were no hidden DTC's. I started looking into problems that other people were having on some forums and people stressed issues with the crank position sensor and coolant temperature sensor. Both made sense to me as to why they would prevent the engine from firing over. I tested my crank sensor, but the plug was in a difficult spot to get a good placement of the test leads. It appeared to be an open circuit across pins 2-3 and this meant, per the service manual, that the sensor was bad. It was cheap, at $25, so I went ahead and replaced it. I was really feeling good about this one as some other people had the same symptoms I'm having and this fixed their problem. Well, it didn't work for me.

I was able to borrow VAG-COM and run an auto scan to check out all the control modules on the car for fault codes. Here is what I got:

Chassis Type: 8N - Audi TT
Scan: 01,02,03,08,15,17,22,35,37,45,54,55,56

Address 01 -------------------------------------------------------
Controller: 8N0 906 018 AN
Component: 1.8L R4/5VT G 0003
Coding: 06710
Shop #: WSC 65728
TRUWT28N521033852 AUZ5Z0B4146046
3 Faults Found:
18010 - Power Supply Terminal 30: Voltage too Low
P1602 - 35-10 - - - Intermittent
17647 - Fuel Injector for Cylinder 3 (N32): Open Circuit
P1239 - 35-00 - -
17648 - Fuel Injector for Cylinder 4 (N33): Open Circuit
P1240 - 35-00 - -
Readiness: 0110 1101

Address 03 -------------------------------------------------------
Controller: 8N0 907 379 H
Component: ESP ALLRAD MK60 0101
Coding: 0022544
Shop #: WSC 01236
1 Fault Found:
00493 - ESP-Sensor Unit (G419)
014 - Defective - Intermittent

Address 08 -------------------------------------------------------
Controller: 8N0 820 043 A
Component: TT-KLIMAVOLLAUTOMAT D03
Coding: 00140
Shop #: WSC 01236
No fault code found.

Skipping Address 15-Airbags

Address 17 -------------------------------------------------------
Controller: 8N1 920 980 E
Component: KOMBI+WEGFAHRS. M73 D14
Coding: 07244
Shop #: WSC 09416
TRUWT28N521033852 AUZ5Z0B4146046
2 Faults Found:
00771 - Fuel Level Sensor (G)
30-10 - Open or Short to B+ - Intermittent
01314 - Engine Control Module
49-10 - No Communications - Intermittent

Address 22 -------------------------------------------------------
Controller: 02D 900 554 C
Component: HALDEX LSC ECC 0010
1 Fault Found:
00526 - Brake Light Switch-F
27-00 - Implausible Signal

Address 35 -------------------------------------------------------
Controller: 8N8 962 267 A
Component: Central Lock/Alarm D06
Coding: 15980
Shop #: WSC 01236
2 Faults Found:
01366 - Opened Due to Crash Signal
35-00 - -
01370 - Alarm triggered by Interior Monitoring
35-00 - -

Address 45 -------------------------------------------------------
Controller: 8N8 951 177
Component: Innenraumueberw. D09
Coding: 00001
Shop #: WSC 00000
1 Fault Found:
01463 - Alarm triggered by Sensor for anti-theft alarm System
35-00 - -

Address 55 -------------------------------------------------------
Controller: 4B0 907 357
Component: LEUCHTWEITEREGLER D004
Coding: 00010
Shop #: WSC 01236
No fault code found.

Address 56 -------------------------------------------------------
Controller: 4B0 035 186 H
Component: concert II NP2 0007
Coding: 00302
Shop #: WSC 00000
1 Fault Found:
00856 - Radio Antenna
36-00 - Open Circuit

End -------------------------------------------------------


The two striking items that stick out to me are the ECM communication fault and the injectors 3 and 4 open circuits. Now these could certainly be causing me some issues, but does the ECM keep all DTC’s stored forever until they are cleared? Would a generic OBD-II scan tool clear these DTC’s? My car is chipped (has been for several years) so perhaps they did not clear the codes after reinstalling the ECM, which could explain the ECM communication fault. Secondly, I did remove the connectors from injectors 3 and 4 to test voltage at the connectors to verify the injectors were getting a voltage signal during cranking, which they were. I need to go back and test them for resistance across the pins to see if I have one or more possibly bad injectors that could be causing my issue.

I apologize for the long write up but this weekend is my deadline for diagnosing this as I’ll be leaving the country for several weeks on business, forcing me to tow it to the dealer. I do still have VAG-COM and can run some other tests if someone has any suggestions. I’ve heard something about the electronic throttle body causing similar symptoms on someone’s car before. Is there any easy way to test this in VAG-COM? I need to read through the Ross-Tech manual and see about this. I’m working with a Bentley service manual as my reference.

I appreciate any help, suggestions, comments you may have. Thank you very much.

DasTT

You can still get a signal at the injector cable harness with the "open" designation. You need to check the injector side which is where the open likely is.

Big turbo TT

Engine RPM speed sensor (G28) or engine coolant temopo sensor are big culprits,even a bad MAF will give you a bad startup,or you have a HUGE vac uum leak.Possibly a crapped out fuel pump or relay

TTuner

I checked resistance across all four injectors and they are good at 12 ohms each per the service manual. I cleared all the DTC's as well and I'm still getting nothing.

I've replaced the Engine RPM sensor so unless I got a bad aftermarket sensor (it tested fine when I got it) that shouldn't be the issue. I'm getting plenty of fuel to the rail so the pump is working.

I cannot properly test the MAF since the car won't actually run, but I did check voltage from pin 4 to ground and it checked out fine at 5.5 V per the service manual so the MAF is getting a voltage. Is there a way to check resistance across any of the pins physically on the MAF?

Also, can anyone point me to instructions on how to test the electronic throttle valve via VAG-COM? I'm searching for this right now as I heard it make a high frequency whine for about 30 secs when I switched the ignition on to check voltage at the MAF.

I'm waiting for a helper to arrive so that I can check a few other things where I need an extra hand (i.e. checking voltages during cranking). I'm about to test the Coolant Temp Sensor as well. Thanks for your replies.

DasTT

Throttle body adaptation can be done by just turning the key on. This could have been the whine you heard.

The car doesn't need a MAF to start.

Next up would be the imobilizer which could be the issue here since you have a no comm DTC with the ECM from the instrument cluster (module 17). The Bentley has some detail on how the imobilizer works. the instrument cluster has to recognize the key in order for it to allow the start. You could have a bad key or it is not adapted to the instrument cluster.

JazziTT

I've been having ZERO (major)problems (knock on wood) and drove to WAWA for a quick breakfast sandwich... Go to start the car and no fire.... Turns over great but will not start... I had a nice walk home (forgot my darn cell phone). Read this post so will get a ride back and try another key before having it towed...

If it doesn't start and I tow it somewhere, I'll post resolution..



Chris

JazziTT

Don't know if it was a fluke or not.. Based on this post's suggestion, I went back to the car with my other set of keys and it fired right up. I'm not convinced though... I tried the 1st set of keys when I got back home and it started with them too... I will replace both sets of batteries (just on principle).. They're the original batteries...

I will now check it with the VAG-COM and see if there are any hidden DTCs..


Are these batteries available from a drug store? Or do I need the dealer?


Thanks for advice... For WHATEVER reason it worked..

Chris

crabriolet

any time you have starting issues check your connectors at the ecm. coolant temp sensor would be second most likely.
creader codes would help and is available for less than 85.00 for the unit.

TTinCT

What is "plenty of fuel at the rail".....??? Did you put a gauge on it and measure pressure? A 225 will put out 60-65 PSI on cold start and settle in around 57 or so when warmed up....just cause the pump is moving gas does not mean it is enough...

That said, based on your symptoms...it sure sounds like an engine speed sensor or a problem at the ECU/Immobilizer....I would check the batteries at the keys and you may need to resync the car with the keys.

Insure all DTC's are cleared by removing the negative battery terminal and let site for a few minutes. Make sure you have your radio codes as the radio may need reprogramming...

Start there...