Questions and Answers

Neon Code 21 Q. Hi, I have a 1997 Dodge Neon 2.0 litre DOHC, 5 speed,100,000 kms.The problem is the car logs a code 21 O2 sensor code on cold starts in the morning or after sitting for a while after driving it. It happens right after turning the key. I changed the upstream O2 sensor but with no luck.

Car seems to run fine with the check engine light on and doesn't appear to be running rich. Help!

A. According to my books, a code 21 is "Engine is cold too long" which means the engine did not reach operating temperature within acceptable limits. This may be due to a bad thermostat of a defective Coolant Temp Sensor. I would check those two items first.

Additional Information provided courtesy of ALLDATA