Limp Mode Diagnosis Guide
This post is written in response to the number of times that TDI owners complain about “lack of power”. It is a supplement to what is contained in the TDIFAQ troubleshooting section, specific to the A3 and B4 cars and is as thorough and systematic as possible, and it is linked to from the general “How-To” thread elsewhere on these forums.
Main symptom: Car lacks power, or temporarily has power but then abruptly loses power under certain conditions. The conditions under which it loses power are generally repeatable.
1. Scan the ECU for codes. DO NOT try to skip this step, otherwise you may end up “barking up the wrong tree” for a long time. VAG-COM or a lookup in the Bentley shop manual result in a text explanation of the codes
a. If you get “Injection start regulation - intermittent”, adjust the mechanical pump timing to get it within specifications as described in the TDIFAQ or the shop manual. If pump timing appears to be within specifications, but the code still comes back after being cleared, check for leaks in the fuel system, because air bubbles can interfere with the mechanism that automatically adjusts the injection timing, and also make sure the fuel filter is good and that the fuel tank contains the proper grade of diesel fuel.
b. If you get the “00575 Intake manifold pressure control difference - intermittent” code, go to step 2.
c. If you get codes related to the catalyst temperature sensors or the supplementary injector pump, you have a hardware problem with those components or a wiring problem related to those components. These codes apply ONLY to a 1996 Passat TDI in North American specification and ONLY to models having the “BK” ECU. Other models do not have the hardware in question and cannot have these codes set. The most likely circumstance leading to these codes is: wrong ECU for the vehicle, wrong catalyst without the temp sensors in the vehicle, wiring harness damaged or not plugged in, deliberate removal or circumvention of the sensors or the electrical portion of the pump.
d. If you get codes related to glow plug operation, these are NOT relevant for power loss situations.
e. If you get codes related to EGR “exhaust gas recirculation” control, clean out the intake manifold as described in the TDIFAQ and perform the recalibration procedure described in the TDIFAQ.
f. If you get codes related to the “mass air meter”, make sure it is plugged in at the harness connector (near air filter) and make sure the wiring is not damaged. Note: this is the MAF sensor. Actual failure of MAF sensors is extremely rare on these vehicles. Do NOT replace the MAF sensor on an A3 or B4 unless all other possibilities of power loss have been exhausted.
g. If you get NO codes, go to step 3.
Get pdf Limp Mode Diagnosis Guide
