ECU Error Codes Unreadable - HELP

Ian Claudi

New member
Joined
Feb 23, 2007
Location
Montreal
TDI
Jetta Wagon 2003
I own a 2003 Jetta TDI Wagon 5 spd manual with 125,000km. The car has been well maintained ( oil, filters, glow plugs etc ) and up until recently was completely problem free.

Note: The car starts easily ( even at -20c ) and I add fuel conditioner to each tank of fuel.

About 2 months ago, the car started suddenly losing power. This is most noticeable on the highway but can happen at any speed. It is now happenning several times a week. When it occurs, it feels like the car has 'magically' transformed from a TDI to a non-turbo diesel. When driving on the highway, it becomes very difficult to pass other cars. Climbing hills requires a downshift.

When the problem occurs:
  • The sound of the engine does not change
  • There is no black smoke coming from the exhaust
  • The glow plug light does not come on
The problem does not occur after starting the car although it can occur within a mile or two of driving.

I took the car to my local mechanic and despite using two different scan tools, he could not read the error codes from the ECU ( although reading other error codes was not a problem ).

My brother-in-law had a similar problem that was traced to a faulty Mass Air Flow Sensor. I changed the sensor on my car but the problem remains.

Two questions:

Where can one find out about the OBD-II wiring harness. Just in case that a wiring harness fault is making it impossible for the scan tool to read the ECU.

Has anyone experienced a similar 'loss of power' problem. If so do you have any suggestions or hints.

------------ Thanks for the responses to my original post ------------------

First - The mechanic, Richard Kirton of Euroservice in Dorion ( excellent mechanic, reasonable prices, helpful advice, endless patience ) used two different VW scan tools, neither of which could read the ECU error codes. Richard's fiirst suggestion was to check all the fuses, which was done. Unfortunately, all the fuses were OK.

Second - I've read some of the posts on 'limp' mode and performed some additional testing. The car can consistently be put into 'limp' mode by accelerating hard for approximately 20 seconds. By turning the engine off and on, 'limp' mode is cancelled and normal performance restored.

Third - The radio is VW stock.

Fourth - I'll check the VNT actuator and the air intake.
 
Last edited:

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
I betcha your mechanic was not using a VW-specific scan tool. A generic scan tool often has problems with VW-specific trouble codes and even when it does read a code, they do not always translate them correctly.

But, I betcha you are having issues with the control system for the turbocharger. (Vacuum leak, faulty check valve, bad N75 valve, seized VNT actuator mechanism, etc. Excessively clogged air intake manifold because of the EGR system can cause this, too)
 

paramedick

TDIClub Enthusiast, Vendor
Joined
Jul 29, 2001
Location
Versailles, Kentucky
TDI
2015 Audi Q5 TDI
True.....just musing. Odd that they can read one, but not the other.

Is there a fuse that protects the ECU side of the port, or the entire port?
 

chrisfiat

Veteran Member
Joined
Jul 14, 2006
Location
farmington nh
TDI
97 jetta
first of all is the check engine light on??? if it not then there will be no codes
have you changed your fuel filter??
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Some boost control problems set a code, set limp mode, but do not set the light. go figure, perhaps the car is a test of knowledge? "Hey buddy, somethings wrong here" is screams with it's limp mode, so doesn't think it has to start that darn CEL that you'll ignore anyway when you turn the car off and on again. I've read this, had it confirmed here, and believe it until I discover otherwise. Or others with experience inform me otherwise.

I believe there is a boost control problem, and it would be nice to find out which one.

Anyone near with a VagCom to test this out? Any aftermarket radio in the beast?
 
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alphaseinor

TDI Innovator Vendor , w/Business number
Joined
Jul 30, 2006
Location
Denton, TX
TDI
'03 Jetta TDI 780,000 miles (totaled out), 01 Audi TT 225 Quattro 230,000 Miles (runs great!), 00 Cabreetle Beetle dash, ALH & MK4 harness Swap
Since you replaced the MAF...

Did you look at your intake?
Does your VNT stick?
any boost leaks?
 

Airliner

Veteran Member
Joined
Jan 15, 2005
TDI
Audi A4 1.9TDi Avant Quattro 2001 silver
chrisfiat said:
first of all is the check engine light on??? if it not then there will be no codes
have you changed your fuel filter??
BULL**** !!

Most of the fault codes will never turn on the CEL.
 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Post in the Quebec forum...

The guys used to get together every Tuesday night at the McDonald's next to the Orange Julep (possibly now at the O.J.)...

See if anyone has a Vag-Com or drive out and see UserID "Wingaman" near Valleyfield...

Limp mode is common...

Yuri.
 

weedeater

Top Post Dawg
Joined
Mar 17, 2001
Location
Reston, VA
TDI
Jetta, 2001, Baltic Green
Considering his mileage (kilometerage?), I would bet on a blocked intake and/or bad MAF.
 

Dimitri16V

Top Post Dawg
Joined
Jan 30, 2005
Location
DE
TDI
01 Golf, 04 Golf
My 01 with a clogged intake would hit limp mode all the time. Cleaned it up and never happened again. there were codes for boost but no CEL
 
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