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Home › Ford › 1988 › LTD Crown Victoria Base, 4D Wagon › Repair and Diagnosis › Engine Performance › System › V8 MCU Control System › Circuit Tests › Code 4-4 THERMACTOR Check

Code 4-4 THERMACTOR Check

  1. Warm engine to normal operating temperature. Upper radiator hose should be hot and pressurized. Turn engine off. Restart engine at curb idle and immediately initiate FUNCTIONAL TEST within 10 seconds and record codes. If any other codes are displayed, go to appropriate tests. If code 11 is displayed, continue with FUNCTIONAL TEST. If code 4-4 is displayed, go to next step.
  2. Turn key off. Disconnect MCU from vehicle harness. Measure resistance from Pin No. 11 (circuit 190) to dump relay Pin No. 3, and from dump relay Pin No. 4 to TAB solenoid. See Fig 1 . If both readings are less than 10K ohms, go to next step. If not, repair open in appropriate circuit.
  3. With key off, measure resistance between dump relay Pin No.s 3 and 4. If reading is less than 5 ohms, replace dump relay and re-test. If reading is greater than 5 ohms, go to next step.
  4. With MCU disconnected, measure resistance from Pin No. 11 (circuit 190) to TAB solenoid. Turn key on to close dump relay contacts. If reading is less than 10K ohms, go to next step. If not, check MCU to TAB solenoid circuit and repair as necessary.
    Fig 1: Positive Thermactor Dump System
    G4235
  5. Reconnect all electrical and vacuum connections. Perform FUNCTIONAL TEST and record codes. If code 4-4 is not displayed, service other codes as necessary. If code 4-4 is still displayed, go to next step.
  6. Remove vacuum hose from TAB valve and connect vacuum gauge to hose. Start and run engine above 2000 RPM for 2 minutes. Stop engine, restart it and initiate FUNCTIONAL TEST. Observe vacuum gauge. If vacuum is always above 5 in. Hg, go to step 8). If vacuum is always below 5 in. Hg, go to step 11). If vacuum pulses above and below 5 in. Hg, go to next step.
  7. Reconnect hose to TAB valve. Remove vacuum hose from TAD valve and connect vacuum gauge to hose. Start and run engine above 2000 RPM for 2 minutes. Stop engine, restart it and initiate FUNCTIONAL TEST. Observe vacuum gauge. If vacuum pulses above and below 5 in. Hg, check and/or service thermactor air system. If vacuum is always above 5 in. Hg, go to step 14). If vacuum is always below 5 in. Hg, go to step 16).
  8. With key off, measure resistance between MCU connector Pin No. 11 (Wht/Red wire) and ground. See Fig 2 . If reading is less than 1K ohms, repair short to ground, and re-test. If reading is greater than 1K ohms, go to next step.
  9. Measure TAB solenoid resistance. If reading is not within 50-110 ohms, replace TAB solenoid and re-test. If code 44 is still displayed, replace MCU. If resistance is correct, go to next step.
  10. Check TAB solenoid output to make sure vacuum is not present when solenoid is de-energized. Disconnect TAB solenoid from vehicle harness. Start and run engine at idle. If vacuum is present, replace TAB solenoid, and re-test. If vacuum is not present, replace MCU, and re-test.
    Fig 2: Thermactor System - Test Connections
    G2521
  11. Turn key off. Check vacuum hose between TAB valve and TAB solenoid for blockage or leaks. If hose is damaged, repair as necessary, and re-test. If hose is okay, go to step 9).
  12. Check TAB solenoid output to ensure vacuum is present when solenoid is energized. Install a jumper wire from TAB solenoid circuit 190 to ground. Start and run engine at idle. If vacuum is not present, replace TAB solenoid and re-test. If code 44 is still present, go to next step. If vacuum is present, go to next step.
  13. Turn key off. Measure resistance between TAB solenoid and MCU (circuits 687 and 190). If reading is more than 5 ohms, repair circuit and re-test. If reading is 5 ohms or less, replace MCU, and re-test.
  14. With key off, measure resistance between circuit 200 and ground. If reading is less than 1K ohms, repair short to ground. If reading is more than 1K ohms, go to next step.
  15. Check TAD solenoid output to make sure vacuum is not present when solenoid is de-energized. Disconnect TAD solenoid from vehicle harness. Start and run engine at idle. If vacuum is present, replace TAD solenoid, and re-test. If vacuum is not present, replace MCU, and re-test.
  16. Turn key off. Check vacuum hose between TAD valve and TAD solenoid for blockage or leaks. If hose is damaged, repair as necessary, and re-test. If hose is okay, go to next step.
  17. With key off, measure TAD solenoid resistance. If reading is not within 50-100 ohms, replace solenoid, and re-test. If code 44 is still displayed, go to step 19). If resistance is correct, go to next step.
  18. Check TAD solenoid output to make sure vacuum is present when solenoid is energized. Install a jumper wire from TAD solenoid circuit 200 to ground. Start and run engine at idle. If vacuum is not present, replace solenoid and re-test. If vacuum is present, go to next step.
  19. Turn key off. Measure resistance between TAD solenoid and MCU (circuits 687 and 200). If reading is more than 5 ohms, repair circuit and re-test. If reading is 5 ohms or less, replace MCU, and re-test.
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