2012 Alltrack Throttle Position Sensor Implausible Signal (P0121)

**gregPearce9876** · 22-01-2020, 07:23 PM

Hi guys,

I have a 2012 Alltrack 2L TDI with 75k on the clock. A few weeks after getting the radiator leak fixed (new pump & timing belt change) by the dealer, the car is now reporting Throttle Position Sensor Implausible Signal (P0121) MIL.

After doing a bit of research, this could be either a faulty pedal or clogged up Throttle body. As a first port of call i would like to clean the Throttle body but i have a few questions:

1. Is this an easy job? I understand that this needs to be 're calibrated' with VCDS (which I am able to do)

2. Does any one have any advice or Tips? The service manual doesn't really detail much.

3. Does the O Ring need to be replaced?

4. Why does the Ross-Tech website say "TDI's do not have throttle bodies"? [ref1]

Thanks in advance,
Greg

[ref1] Throttle Body Alignment (TBA) - Ross-Tech Wiki

**kamold** · 22-01-2020, 07:56 PM

Unplug the pedal connector and spray some contact cleaner in, plug it back in.
Try that first.
Diesels don't have a throttle body.

**gregPearce9876** · 22-01-2020, 08:46 PM

Thanks for the reply Kamold.

Please excuse my ignorance, but what are these people referring to when they say 'throttle body'?

YouTube

Throttle Position Sensor (G69) - TDIClub Forums

I trawled these forums over many months before buying my car enough to understand that you know what you are talking about.

**gregPearce9876** · 01-03-2020, 01:02 PM

Quick update.

There is some confusion online about the throttle valve (as Volskwagen Call it). This valve controls the air flow to the EGR system as well as acting as a anti-shudder valve for a smooth engine shutdown.

The P121 Code is a reading out of range signal from the potentiometer connected to the valve. In my case, the valve was not closing quickly enough, which caused the code to appear during shut down.

I pulled the valve off and gave it a clean with some throttle body cleaner. Shut down is much smoother, and the code has not returned (3+ weeks later).

For anyone with this code, its a very messy but easy job to do. I can also confirm that there is no coding / calibration required when the valve is reinstalled.

Before: