Crankshaft Relearn Ability

In order to correctly detect misfires, the PCM must learn the variation between the 7 crankshaft notches. This procedure is performed only once. However, if the crankshaft is replaced, the crankshaft variation must be performed again. This can be accomplished using the Scan Tool or Service Stall System (SSS). The following is a description of what happens when this procedure is performed.

When the procedure is initiated, the Scan tool or SSS will send a message to the PCM to reset the CRANK LEARNED adaptive to NO. After this is accomplished, a delay counter in the PCM will remain constant until all misfire enable criteria has been met or MISFIRE ENABLED is set to YES. If vehicle speed is present or if TP angle is greater than 2.3% when CRANK LEARNED adaptive = NO, the delay counter will increment and the ignition will have be cycled Off for 10 seconds to reset the counter. The procedure would then have to be repeated.

As soon as MISFIRE ENABLED = YES when CRANKSHAFT LEARNED = NO, no misfires can exist. The PCM will then start to decrement the delay counter down to zero, which will take two engine revolutions. Once the delay counter is at zero, a 400 revolution test at idle is performed to determine if the engine idle is stable enough to perform the relearn procedure. At this time the PCM determines if any misfires are present.

If one misfire occurs during the 2 + 400 revolution test, the PCM will not learn the crankshaft for that ignition cycle. The ignition will have to be turned Off for 10 seconds and the entire procedure repeated.

After the PCM has run the 2 + 400 revolution test without any misfires, the SERVICE telltale will flash. The PCM will then wait for the engine RPM to be raised between 3000 and 4000 rpm. After the rpm is raised, the PCM will then take two crankshaft revolutions to learn the crankshaft variation. The entire learning process is done only with these two revolutions.