My 1989 Sierra K1500 5.7L, V8, Vin (K), 4 WHD, 150K miles, starts up fine when when cold, but when it gets hot, it stalls and won't start again until it cools off (it turns over fine when it's hot but won't start). Sometimes I can get it to start, but only if I press the accelerator to the floor and it will buck like it's running on half the cylinders. The "Check Service Light" is always on, so I put a paper clip in the Data Link Connector's pins A and B and got several codes. I got code 12 (diagnostic mode), code 15 (coolant temp/low temp) and code 45 (O2 sensor/exhaust rich). Any suggestions? From previous owner's records from 96K miles to 150K miles, the fuel pump was changed at 122K miles but I have no record of the fuel filer being changed between 96K miles and 150K miles.

Thanks.....Steve

Welcome to AF. I'd replace the coolant temp sensor, the engine codes show it is running rich, try this for starters. Watch for raw fuel in the oil as a result.

Thanks Max. I have just bought a replacement coolant temp sensor and will put it in the Sierra truck this weekend. I'll let you know if the sensor fixes the stalling at hot temperatures. I only use the truck occasionally as an off road vehicle including snow plowing.

Replacing the coolant temp sensor did fix the truck stalling at hot temperatures.

Thanks Max. You were right on.

-Steve-