Show 0% when the throttle is closed?

RLITWITZ

MEMBER
2001 CHEVROLET PRIZM
4 CYL
2WD
AUTOMATIC
110,000 MILES

The Throttle Position Switch on my 2001 Prizm (110,000K miles) shows 10% on my scan tool when the throttle plate is closed. As far as I can tell there are no opens or shorts and the voltage and resistance change smoothly (no dead spots) as I advance the throttle manually (engine off in run). My Haynes book doesn't help much. With the (large) resistance range it quotes I should be OK.

Is this normal/acceptable for this vehicle? All other cars that I've scanned show 0% when the throttle is closed. The manual says it's not adjustable and that the computer self-calibrates at idle w.R.T. The reference voltage.

I ask because the long term trim is more than 10% rich. I noticed this TPS quirk when diagnosing my O2 sensors. I periodically get a MIL light with a 420 code. It's the only one and I have no overt drivability problems other than fuel efficiency. I get ~26 mpg in short hops and haven't been on any long trips lately.

I'll find/fix whatever's wrong with the CAT/O2 system,
but I'd like to resolve this question first.

Thanx

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

For this vehicle the acceptable range is 8% to 12%. So being at 10% is normal.

The P0420 code is for the catalytic efficiency below threshold. It can be due several factors. This code can also be triggered due to the engine running rich. Which can be a issue with the oxygen sensor.

I have attached the diagnostics for the code P0420. Go through that step by step process and you should be able to pin point the issue.

https://www.2carpros.com/trouble_codes/obd2/p0400

Please let me know of any questions.
Thank you.

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