Electronic Control Unit (ECU)
- Connect negative lead of voltmeter to ground near ECU. Check for battery voltage at terminal No. 18 of ECU harness connector with ignition on. See Fig 1
. Battery voltage should be present. If battery voltage is not present, check fuse No. 22 (900 Series) or fuse No. 13 (9000 Series). If battery voltage is measured, go to next step.
Courtesy of SAAB-SCANIA OF AMERICA, INC.
- Using a test light, check ECU ground connections. Connect test light between terminal No. 18 and terminals No. 5, 11 and 25. With ignition on, test light should illuminate at all 3 terminals. Ground connections are located on cylinder head and engine lifting hook.
- Connect test light between terminal No. 1 of ECU harness connector and ground. Test light should pulse when engine is cranking. To check power output to ECU, ground ECU harness connector pin No. 21 and check voltage at pin No. 9. Twelve volts should be present and relay operation should be heard.
- Ground pins No. 21 and 17 at ECU harness connector. Check voltage at GRN/RED wire (900 Series), GRY/RED wire (9000 Series) of 3-terminal limp-home test connector (connector is located near evaporator housing). Battery voltage should be present. If voltage is okay, pump and system relays are operating properly. Proceed to COOLANT TEMPERATURE SENSOR test. If voltage is not okay, go to SYSTEM RELAY TERMINALS test.