Hello. I have a new code that I need help with. But first the patient's vitals. It is a 2007 HHR, 2.2l, auto., 278,000 miles. I have a check engine light showing and went to Autozone for a scan. It came back code P0121 TPD Circuit Range/Performance with secondary codes P1818 and p1818-00 transmission fluid sensor. The recommendation on the sheet that Autozone gave me is to replace the whole TBI Unit. I am just wondering if this is totally necessary to do or if there are any other fixes or causes for this code? I love my little HHR and it has treated me well so far. If I do need to replace it should I risk a junkyard part until I can afford a new one or just try to save the money back to go new? I value everyone's opinion. Thanks in advance. God bless Y'all. Stay safe and healthy. Happy Thanksgiving.

 

Welcome to the site! code P0121 may mean that one or more of the following has happened:

TPS has intermittent open or short internally

Wiring Harness is rubbing and causing an open or short in the wiring

Bad connection at the TPS

Water or corrosion in connector or sensor


If you clean the throttle body be extra careful to not move the throttle plate , the plastic gears are easy to strip.
You should be able to bolt on a used throttle body, but I’d suggest cleaning yours first!
Use a quality spray cleaner like CRC throttle body cleaner, not WD40 or brake parts cleaner!

P1818 The TCM detects a PARK, NEUTRAL, or a drive range with a REVERSE ratio for 3 seconds.

This means this code could be set by putting your car in drive while it is still backing up. Always bring your car to a stop before shifting to drive. It could also be set coasting down a hill or driveway backwards in neutral for more than 3 seconds.

I would clear the code and see if it does it again in normal driving.

 

Any chance the CEL came on just after an air filter change? Other thing that might cause P0121: bad/disconnected MAP or MAF.
Oddly, P1818 could be related. Might be a loose electrical connector or frayed wire or loose or broken Park/Neutral switch
It might also disable auto door locks, cruise control and the shift interlock

 

Update. A day after the CEL illuminated it went out again. The auto. Door locks had indeed stopped working and now 3 days past they are again operating. Should I still be concerned about the original CEL activation and subsequent code? Thanks again.

 

I would relax and be careful when shifting in and out of reverse. Maybe look for frayed wires and loose connections under the hood.

 

Thanks.

 

Random electrical weirdness suggests a dying battery, epecially with the onset of cold weather. But with that many miles, having a look at the throttlebody and probably cleaning it is a pretty good idea anyway. Clean the MAF sensor too.