fixing P0121 code for smog certification

Old 09-20-2007, 04:18 AM
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Join Date: Sep 2007
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Default fixing P0121 code for smog certification

i had a problem where my stick shift 2001 vw cabrio (driven for 90k miles) stalled while driving at 40 mph & would not start again. i got it towed to a AAA repairshop who replaced the spark plugs , wires , router, distributor and ignition coil. [/align]the car again died on me after 10 days for the same problem where ignition coil went dead again.[/align]this time the repairshop spent some more time on checking Check Engine light & ECM which was spitting the P0121 code. that code relates tothrottle position sensor malfunction & therepairshopreplaced the Throttle Body costing 600$ and the Check Engine light still does not go off.[/align][/align]Now my questions:[/align]1> Do we need to really replace the Throttle Body or is it of any value in cleaning at 90 K miles. What is the schedule for changing it?[/align]2> The CL light came on when I had to change the dead battery on my car ( 6 months before this incident). Would cleaning the Throttle Body and adapting the throttle reslove the issue or replacing it is advisable?[/align]3> the Repair guy says the resistance measured on multimeter on the older Throttle Body is quite high compared to newly replaced Throttle Body, this is addition to smoother idlying on changing to the new one confirms that Throttle Body does need to be replaced. is this correct?[/align]4> The Code P0121still has not gone and he says that it would need to be adapted by a VW shop to get it cleared. [/align][/align][/align]Any suggestions , please?[/align]
Old 02-24-2013, 02:44 PM
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I know this is an old thread but want to help out the people like me that stumbled upon it and want to know what the answer is. When the P0121 code comes up it does NOT mean the throttle position sensor is bad or to replace the throttle body. It means that the computer has lost the programming stored in an erasable memory. Almost all the time it was because the battery has died or the battery was changed and took a while with the battery disconnected and lost the info.

The way to fix it is to take it to a dealer or a shop that has a VW programming scan tool. Not just a cheap OBD II reader. When the engine memory goes it usually also throws a P1544?? code for the automatic transmission for a loss of memory there also. The usual charge may be around $60 depending on the shop. It only takes a couple minutes. Seems like a common VW problem. BTW it makes the car run quite rough.
Old 02-24-2013, 07:11 PM
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VAG Error Code: 16505
EOBD II Error Code: P0121

Fault Location:
Throttle Position (TP) Sensor (G69)/Switch A/Accelerator Pedal Position (APP) Sensor/Switch (G69) A - Implausible Signal

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) Triggered on first occurrence.
Poor engine performance.

Accelerator cable adjustment.
Throttle position (TP) sensor/switch.
Accelerator pedal position (APP) sensor/switch.
Wiring Harness issue.
Failed Throttle Body.
Failed Engine control module (ECM).

Possible Solutions:
Test wiring as per Factory Repair Manual

Special Notes:
For some vehicles, there may be a TPI with instructions on replacing the terminals for the throttle body.
Some ECMs may have a firmware update to address this issue during cold weather.

VAG Error Code: 17952
EOBD II Error Code: P1544

Fault Location:
Throttle Motor Position Sensor 1 (G187) - High Input

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) Triggered on first occurrence.
Wiring short to positive.
Throttle motor position sensor.

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