G 2500 3/4 Ton Van V6-262 4.3L VIN Z (1992)
Torque Converter Clutch (TCC) Circuit
Circuit Description:
The purpose of the automatic transmission Torque Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter stage
when the vehicle is in a cruise condition. This allows for the convenience of the automatic transmission and the fuel economy of a manual
transmission.
Fused battery ignition is supplied to the TCC solenoid through the TCC brake switch. The ECM will engage TCC by grounding CKT 422 to
energize the solenoid. TCC will engage when:
^
Vehicle speed above 30 mph (48 km/h)
^
Engine at normal operating temperature (above 65°C 149°F)
^
Throttle position sensor output not changing, indicating a steady road speed.
^
Brake switch closed
^
Third or Forth gears
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
1. A test light "ON" indicates battery voltage and continuity through the TCC solenoid is OK.
2. Checks for vehicle speed sensor signal to ECM using a "Scan" tool.
3. Checks for forth gear signal to ECM. This signal will not prevent TCC engagement, but could cause a change in the engage and disengage
speed points.
Diagnostic Aids:
Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "driver". See: Powertrain
Management/Computers and Control Systems/Testing and Inspection/Component Tests and General Diagnostics/ECM QDR Check Procedure
(Without 4L80E) With 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 resistance.
To prevent TCC overheat condition, TCC temperature closes at 279°F +/- 7° and reopens at 259°F +/- 9°.
