ECM Replacement Check

Many test procedures and test charts in the ENGINE PERFORMANCE Section lead to conclusion that ECM is faulty. Before replacing ECM, check driven circuits and ECM quad-drivers using following procedures and accompanying flow chart. See Fig 1.

1. Using a DVOM, backprobe ECM drive circuit in question and measure pin voltage with ignition on. If system voltage is present, go to next step. If system voltage is not present, turn ignition off. Disconnect ECM connector. Measure voltage on connector terminal for suspect circuit. If low voltage is measured, check circuit for an open or short to ground. Repair as necessary. If system voltage is measured, ECM is defective.
2. With DVOM still backprobing ECM at suspect circuit, ground ALDL "test" terminal "B". Monitor voltage drop on circuit for at least 2 minutes. Voltage drop should not be greater than .5 volt. Some circuits may have low voltage until ALDL "test" terminal is grounded. A "switching" operation should occur. Some TCC systems have pressure switches in series with TCC solenoid. On these applications, complete this circuit by disconnecting transmission/transaxle connector and using a standard test light in series between terminals "A" and "D" of connector.
3. If voltage drops and then floats back up, this occurs when QDR circuit is going into current limiting. Check the circuit current flow (.75 amp maximum, except as noted in QDR check chart).