05 Sunfire Code: P0128

[OriginHacker21]

Need some advice here. Sister has an 05 Sunfire (41,000 miles). She drives it very poorly (floors it upon start). Anyway, she recently got a Check Engine light. I (being the family mechanic) looked at her car. 1. Engine oil was black as soot (only has 4k miles on it - Pennzoil Platinum 5w30). 2. Air Filter was like a brick of black dust (Fram)

. Other than that, coolant was fine, oil level, and everything else ok.

The code (from what ScanGuage tells me) is P0128. Looking up on websites it means : "Engine Coolant Temperature Below thermostat Regulating Temperature." P0128 - "Under driving conditions thermostat regulating temperature should be achieved based on amount of cumulative airflow ingested and based on startup coolant temperature."

Now, not being a mechanic - that tells me maybe a stuck thermostat or not enough airflow to engine? I drove her car for 5 minutes - temperature went up just fine. I just got done changing her oil (captured some in a used oil analysis bottle) and replacing her air filter. I'm putting the last quart in as we speak.

Advice, Comments, anything? She has the extended warranty so if this engine light doesn't go out after what I've done - I'll tell her to take it to the dealer. Thanks - Paul

 

[OriginHacker21]

Oh, I accidentally hit clear on the ScanGuage so now her engine light is off.

Hopefully if that is an issue it will turn the engine light back on.

 

[wavinwayne]

Stuck open thermostat, or defective Coolant Temp. Sensor would be my first guess.

 

[OriginHacker21]

So will she be ok driving it around? Or should I tell her to get it to the $tealership ASAP?

 

[wavinwayne]

If it's under warranty, & she has kept up her end of the warranty agreement, I'd suggest to her that she take it to the dealership asap.

 

[benjamming]

She will have to wait until the light comes back on before they will attempt do anything that would remotely be considered helpful.

 

[rpn453]

It's nothing critical. I would have cleared the code and only taken the car in if it returns anyway.

 

[OriginHacker21]

I cleared the code - and it has not yet come back on (after a good 6 hours). I guess if it doesn't come back on there is nothing I can do at the moment. Either way - many thanks to the posters for the information and help

. Maybe it was the badly plugged up air filter restricting air flow?

 

[Gary Allan]

The code may or may not come back until another cold start event. Stick your scan tool on there (no light) and you may see a pending code.

 

[TexasHonda]

If the temp sensor is reporting a temperature too low for the fully warm engine, the ECU may set CEL to check for possible faulty engine coolant temp sensor. ECU may have other engine temps to compare with the engine coolant temperature, allowing it to infer the engine coolant sensor is faulty.

Your scan gauge may be able to monitor engine coolant temp. If internal car temp gauge is normal and coolant temp is low, perhaps < 150F then coolant temp sensor for ECU must be replaced.

good luck