VWVortex.com - 2001 Jetta 2.0 Throttle / Pedal Position Sensor & Catalyst Efficiency (P0420, P0226, P2138)
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    Thread: 2001 Jetta 2.0 Throttle / Pedal Position Sensor & Catalyst Efficiency (P0420, P0226, P2138)

    1. 10-14-2009 04:44 PM #1
      So I've had my wife's 2001 Jetta 2.0 up on jack stands for the past couple weeks waiting for parts. I took it to the dealer last month for a CEL that gave code P0420 at AutoZone. I don't have a VAGCOM so that's the best I could do. Before throwing parts at it, I took it to the local dealer and they were able to read a total of four codes, two of which indicated a failing pre-cat O2 sensor. I elected to replace it myself rather than shell out $800 for parts & labor on top of the $58 diagnostic fee.
      ********************** claimed that the appropriate O2 sensor for a 2001 Jetta 2.0 was a universal four-wire. I ordered it before checking the car (duh), and it turns out the pre-cat sensor is a five-wire. So I searched their website for what looked like the best match, and bought a five-wire Bosch sensor with an OEM plug that matched the Jetta. After an overnight soak of PB Blaster and waiting for a slotted O2-sensor socket to arrive, the crusty old O2 sensor came out with very little effort. I replaced it, then took the original four-wire sensor the website sent me and spliced it to the post-cat O2 connector. All the wire colors matched on both cables. So now I have two new O2 sensors to measure the exhaust cleaning properties of the catalytic converter that the dealer assured me is in working condition. While it was up on the stands, I took a few minutes and changed the oil to Mobil 1 synthetic and replaced the oil filter.
      Buttoned everything up and hopped in the car only to be greeted by another dash light. Now instead of just the CEL, the EPC light is on. Perfect. Limped the car to AutoZone (I know, I know), and not only is the P0420 code still there, but now I have two codes related to either the throttle or pedal position sensors: P0226 and P2138. I'm only getting partial throttle from the engine even when the pedal is on the floor. What in the world could I have done to cause these two codes to pop up while replacing the O2 sensors and changing the oil?
      Should I check the TPS to see if I damaged any wires? Is it worth taking a look at the pedal sensor too? What about disassembling the sensors and cleaning them? I can't fathom a way that the cat and the TPS would be related.
      I recently replaced a coolant flange on my 2003 GTI 1.8T, and it's running well except for an intermittent hesitation in acceleration between 2000 and 3000 rpm. I'm new to VW ownership, and it seems like I've been doing nothing but trying to fix these cars since I bought them in August.
      Any help or advice would be much appreciated.

    2. 10-25-2009 01:48 AM #2
      Follow up: autopartswarehouse dot com does not indicate the appropriate O2 sensors for a 2001 Jetta 2.0. First, the generic they claimed matched the front had only four wires, not the required five. Second, when I tried to use it to update the rear O2 sensor (that was working, I just figured I'd use the part), it tripped the EPC light. I didn't put two and two together, but it should have been obvious since the light didn't come on until I changed the rear O2 sensor. I just got thrown off by what the Autozone OBD II reader claimed was the problem. Like everyone else says, Autozone codes are just plain wrong. I spent $120 at the dealer just to get it properly diagnosed. They wanted $380 to install a factory rear O2 sensor! The problem had nothing to do with the pedal or throttle position sensors. The problem was that the generic sensor was supplying 12V back to the system. I had no idea that the return voltage passed through the Transmission Control Module, but the TCM dealt with those 12 volts for days as I drove the Jetta around. The tech said it was a miracle the transmission was still working. Long story short: don't trust generics. Only use Bosch OEM O2 sensors on your VW, or you're asking for trouble. The extra $30 will save you from a $1200 TCM replacement. Lesson learned. I'm hoping the factory part, which arrives tomorrow, will clear up the CEL and everything will be good on the Jetta. For now. Meanwhile the dipstick tube on the GTI shattered, I can't find the leak in the washer fluid reservoir, and coolant is leaking again even though I just replaced the notorious coolant flange.

    3. 12-21-2010 12:22 PM #3
      P0420 is the code for the catalytic converter. I had the same problem and replaces the O2 sensor. The light came back on. I took the car to my Uncle who owns a repair shop and he said Autozone gave me the wrong reason. I replaced the converter and the light went out.

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