Stoney

Our 1997 A4 1.8T has an intermittent failure to accelerate... the engine just doesn't rev when pressing the pedal. We don't know the cause. Turbo was recently replaced, and carbon flushed from cylinders. Did not fix it.

I found a fault code in the transmission (auto, pre-tip) that says "brake light switch, unplausible signal" for which the repair instructions are to look for shorts or for a faulty switch.

If I put my left foot on the brake slightly, enough to trigger the brake light, and accelerate from a stop, the engine fails to spin up much. This may be an interlock to prevent "unintended acceleration." So it seems plausibly the cause.

Are there more than one brake light switch? Or, is just one switch used to control the brake light, the transmission interlock (the brake symbol on the transmission bezel), and the accelerator interlock?

One possibility is perhaps there is oil or water in the electrical connector to the tranny. This happened 2 years ago, and left the tranny in "limp mode." Blowing it out (and clearing the codes) solved that.

Thanks for any experience you guys may have. (Of course, another possible cause of the acceleration problem may be a hose or BPV, which we will check next.)

<img src="http://pictureposter.audiworld.com/230/code00526brakelightswitch.jpg">

Notes to the above table: UPDATE: These seem to suggest that this may be a harmless, erroneous fault code, not a valid fault:

1) This type of malfunction is indicated on VAG 1551 in addition to the affected component.

Note to DTC code 00526:

* The malfunction appears when the ignition is switched on and after one time activation of brake pedal, if the Brake Light Switch -F- is OK , erase it .

* Before activating the DTC memory, press brake pedal briefly, so that the stored malfunction is erased

Kris Hansen

I don't know, but I have that code now too.. My car accelerates fine.

Paul H. (near Annapolis, MD)

Before you turn on the key (ignition), step on the brake pedal. Don't release it until about 2 seconds after turning on the ignition.

Failure to do this on my '98.5 will cause a DTC from the transmission - Brake Light Switch - Incorrect Signal. This is documented in the Service Manual...somewhere (don't have mine handy), and is completely normal.

If the DTC remains after doing the above, then chances are you do have a problem.

Paul

Kris Hansen

Interesting.. Maybe the transmission is looking for that signal at startup...

Paul H. (near Annapolis, MD)

The DTC I am talking about is for diagnostic purposes (informational) only. I wish I could remember the specific DTC number. And it will only be present in the transmission controller. Failure to depress the brake pedal at startup will not affect the operation of the engine or transmission.

I once reported this DTC to my dealer, and they showed me the reference in the service manual. I do not recall seeing a similar reference in my Bently CD manual.

Paul

Kris Hansen

00159? (I think that's the one...)

Stoney

They seem to suggest that this may be a harmless, erroneous fault code, not a valid fault:

1) This type of malfunction is indicated on VAG 1551 in addition to the affected component.

Note to DTC code 00526:

* The malfunction appears when the ignition is switched on and after one time activation of brake pedal, if the Brake Light Switch -F- is OK , erase it .

* Before activating the DTC memory, press brake pedal briefly, so that the stored malfunction is erased

Paul H. (near Annapolis, MD)

This is exactly what I was referring to, yes.