Codes P0300, P0463 and P0128

LEELEE_29

MEMBER
2006 CHEVROLET MALIBU
2.2L
4 CYL
2WD
AUTOMATIC
226,000 MILES

I had a buddy of mine run a test through on my car and it was throwing up p0300 p0463 and p0128. I was wondering since you've worked in GM so long and seem to be pretty knowledgeable what you think the problem most likely is causing all those codes. My car to roughly idle really bad and barely make it point to miles down the street one week then 2 weeks later it makes it all the way like a 20 minute drive and 20 minutes back without a hiccup with a slight misfire terrible fuel mileage as well used to get like 26 miles to the gallon. Now I'm only getting like not even 17, but no smell of fuel, no leaking from anywhere in or around the engine. I could really use your advice guys. Thanks.

2 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The P0300 indicates a random misfire. The P0463 is related to the fuel gauge. The one that is the likely problem is the P0128.

The code indicates an issue with the engine coolant temperature sensor. This sensor is used by the vehicle's computer to determine the needed air/fuel mixture for the engine to run properly. For example, if in error, the sensor tells the computer it is 40 degrees below 0, the computer reacts by adding fuel to the engine's air/fuel mixture. If it is actually 70 degrees, the engine will be running very rich which results in the symptoms you described.

So, if the scanner your friend has can read live data, have him check two things. First, when the engine is cold, have him check the ECT signal to the computer. The temperature indicated should be very close to the ambient temperature when checked.

Next, have him check the short-term fuel trims when the engine is running and let me know what they are.

I will watch for your reply.

Take care,

Joe