Have 90 silverado. new heads, plugs, O2 senser, somewhat ...

Unless your check engine light is coming on, you won't have any codes but here's the proceedure.

To extract a trouble from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.

Ground terminals A and B with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A 12 consists of one flash, a short pause, then two flashes in rapid succession.

After 12 is displayed, any stored trouble s will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All s are displayed 3 times each then a 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.

Images available only to Customers.

The ALDL diagnostic connector is located in the passenger compartment.

HEY THERE HAMMER. THANKS FOR THE INFO. UNFORTUNATELY LOOKS LIKE WE'RE COT FINISHED YET.
REFERRING TO ATHE HAYNES MANUAL I CHECKED THE VOLTAGES TO THE THROTLE POSITION SENSER AND FOUND THEM WAY HIGH AT IDLE POSITION AND LOW @ FULL THROTLE. ENGINE BEHAVIOUR HAS NOT CHANGED.
FINALY WAS ABLE TO UNDERSTAND CODS AND WHAT THEY MEAN. AFTER REPLACING O2 SENSOR, TPS, AND COOLANT SENSOR/ECM/PCM I'M GETTING 44 CODE (ENGINE LEAN)GOT CONTINUETY FROM O2 LEAD TO GROUND BUT NO VOLTAGE AT O2 LEAD COUPLER. I'M ASSUMING ECM ITSELF IS OK SINCE THERE IS NO 55 CODE COMMING UP ONLY 44.
ANY AND ALL IDEAS GREATLY APPRECIATED.
CHARLES
90 SILVERADO

I seriously doubt you needed half of that stuff. Code 44 simply means lean exhaust. That doesn't mean there is anything wrong wiith the sensor or computer. It can very well be telling you the truth and be as simple as a vacuum leak. You need to monitor the voltage at the O/2 sensor with the engine running. It's supposed to continuously cross for below .500 to above .500 up to about .900 and back down again. Monitor the voltage and if it's staying below .500, squirt a shot of carb cleaner into a vacuum line or something and watch for the sensor voltage to spike. That will mean the sensor is working fine and you need to look for the cause of a lean condition. Vacuum leaks are the most common cause. A bad MAP sensor or low fuel pressure can also do it.

Edited by Hammer Time on October 17 2005 at 6:30pm