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AutoFocus: Learning how to 'relearn' on a cranky 2004 Chevrolet Aveo

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AutoFocus: Learning how to 'relearn' on a cranky 2004 Chevrolet Aveo

Vehicle: 2004 Chevrolet Aveo 1.6 VIN 6 engine, automatic transmission.

Symptoms: Malfunction Indicator Light (MIL) was flashing with code P0300. Scan data shows no misfires and no other codes. The vehicle history shows that the engine was overheated and driven until the engine stopped running. A used engine was installed. The shop replaced the oil pan, timing belt, water pump, thermostat and housing. They also swapped spark plugs and the coil pack.

When the shop called our Repair Hotline, I recommended a General Motors procedure relating to code P0300 after crankshaft or engine replacement. I asked the technician to disconnect the battery, hold the cables together for 15 minutes, reconnect the battery, and then test operation. A “Crankshaft Position Variation Learn” procedure with the scan tool was also recommended.

GM has an updated procedure that requires the latest version of the scan tool software. Service information states that after the initial set-up, this message will flash: “Test in Progress,” and then while progressing through the procedure, this message will appear: “Accelerate to Wide Open Throttle.”

While the Test in Progress message is flashing, make sure the transmission is in “park” and the brakes are applied. Then accelerate to wide-open throttle and hold at rev limit until the message is displayed: “Learned This Ignition.” Release the throttle. During the wide-open throttle, the RPM will vary from 1000 to 4000. Another relearn attempt is not allowed until the scan tool and ignition switch are turned off for at least 30 seconds.

The technician’s scan tool would not do the relearn procedure; it did not even offer this function. During road testing and attempt to do relearn, the transmission would not shift into fourth gear. There is no mention of fourth gear inhibit for code P0300 or if Crankshaft Position Variation Learn is not done.

The vehicle was brought to Identifix for a Crankshaft Position Variation Learn procedure using a Tech 2 scan tool. During scan tool set up, the Tech 2 scan system found codes P0300 and P0700 in the engine control module. Code P1781was found in the transmission control module.

After clearing all trouble codes, the technician did a Crankshaft Position Variation Learn procedure. The procedure was fully prompted on the scan tool. The technician repeated the procedure five times. After the fifth repetition of rev limit, the engine lurched momentarily on deceleration from rev limit, and then returned to idle. The “Crank Learned Status” switched from “Not Learned” to “Learned.”

During the test drive, the MIL stayed off, no codes set, and the transmission shifted into fourth gear. It appears that the transmission code had been inhibiting 4th gear. The codes that were not displayed on other scan tools created the confusion of the transmission not shifting to fourth gear. The Tech 2 scan tool did the learn procedure with no problems. There may be some software variation in other scan tools that prevents enabling the learn procedure.

(For more information on Identifix, visit www.identifix.com.)

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