Chart C8-A, Torque Converter Clutch Electrical Diagnosis - 1991 5.7L PFI Y Body: Notes
The purpose of Torque Converter Clutch (TCC) feature is to eliminate power loss of torque converter stage when vehicle is in cruise condition. This allows convenience of an automatic transmission and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid. TCC will engage solenoid when vehicle speed is greater than 24 MPH, engine is at normal operating temperature, throttle position sensor output is not changing (indicating a steady road speed), and brake switch is closed.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Confirms 12-volt supply as well as continuity of TCC circuit.
- Grounding the ALDL "test" terminal with ignition on and engine off should energize the capability of the ECM to control the solenoid.
- Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure to the ECM "quad-driver". Using an ohmmeter, check the solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM. Replace any solenoid or relay that measures less than 20 ohms.