imgolfing4

1998 Audi A6, last week "check engine light" came on, seemed like it was shifting hard between 3rd and 4th. Didn't drive it for a week, seemed like the trans was slipping at low speeds <40mph. Took it for a test drive yesterday, and seemed to be running fine, until I went from interstate to ramp and while slowing down the trans went into safe mode, the PRND432 was lit up solid and seemed like I only had reverse and fourth gear. Stopped at a repair shop and by the time they were ready to look at it, the problem went away. I've attempted to read the OBD codes three times with three different devices, all three can't connect to car. Prior experience suggests ECU. Checked TCU and all appears to be fine. Checked trans fluid, added maybe a pint, not much.

Harleyguy

Yes your car went into limp mode. First you need a code reader compatible with VW/ Audi. Some will read engine codes but not ABS or transmission codes. If you do a search on this website you will find mant threads on here dealing with this problem. Check the transmission control module for water incursion/ damage. This is probably the most common cause of your reported problem. Especially if it is intermittent. Could be at the connector or internal to the module. If you have gone into limp mode then there should be fault codes stored in the system. Find a code reader that will work with your car.

imgolfing4

The TCU was removed and visually inspected, exterior and interior of protective cover are pristine. Tried three (3) different code scanners, including a Bosch unit specific for European autos, none were able to connect to the ECU. Is there another method to download faults besides onboard obd port?

Harleyguy

Even Bosch scanners for European vehicles will not necessarily read VW/ Audi. You will need to find a scan tool that is specified to read VAG COM vehicles. The generic scanners at some auto parts stores like Autozone can usually read the basic (check engine light codes) but not usually ABS or transmission faults. Many manufacturers have scanners specifically for VW/ Audi. Mac Tools, Snap On, etc. have scanners that will do the trick if the owners have purchased the software for VW/ Audi. The experts on here recommend Ross Tech. You buy their connector cable and a software license, hook up your lap top (Windows only. Not compatable with Mac.) and have at it. Alternative #2 is get the car to a shop that has the capability to do the scan/ diagnosis.