Fault Isolation Procedure
- Checking the coolant: If the coolant level is so low that the coolant can not be seen in the reservoir, top it off and go to step 12, otherwise go to next step.
- Checking the antifreeze: At outside temperatures below 0°C, check the freezing point of the coolant. If the coolant has frozen take steps to rectify the fault and go to step 12, otherwise go to next step.
- Checking the thermostat:
- Let the engine cool down so that a hand can be put on the cylinder head without getting burnt.
- Check the temperature of the cylinder head with an external temperature gauge.
- Start the engine and run it at idling speed.
- Place your hand on the upper radiator hose near the thermostat to check whether the hose grows hot quickly when the temperature of the coolant approaches 89°C and the thermostat opens.
If the coolant temperature remains fairly constant 85-95°C for a minute or so, go to next step, otherwise go to step 11.
- Checking the sensor's grounding:
- Unplug the connector: Coolant temperature sensor (202).
- Connect Test Lamp (86 1 857) to B+ and pin 2 of the female connector (black).
- Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic tool while doing this.
If the test lamp illuminates, go to step 6, otherwise go to next step.
- Rectifying the lead: The lead from crimp connection 17 (black) to pin 2 of the female connector is faulty. Rectify the fault and go to step 12.
- Checking the control module's sensor input:
- Turn the ignition switch to the ON position.
- Contact ECM.
- Read value: Coolant Temperature.
- Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic tool while doing this.
If the reading shows -40°C, go to step 8, otherwise go to next step.
- Rectifying the lead: The lead from pin 2 (white/green) of the female connector to pin 39 of the control module is faulty. Rectify the fault and go to step 12.
- Checking the control module's sensor input (continued):
- Connect a jumper lead between pins 1 and 2 of the female connector.
- Read value: Coolant Temperature.
- Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the wiring harness. Observe the multimeter, test lamp or diagnostic tool while doing this.
If the reading shows 160°C, go to step 10, otherwise go to next step.
- Rectifying the lead: The lead to pin 39 (white/green) of the control module is faulty. Rectify the fault and go to step 12.
- Changing components: Change the coolant temperature sensor. When finished, go to step 12.
- Changing components: Change the thermostat. When finished, go to next step.
- Checking temperature:
- Read value: Coolant Temperature (ECM).
- Check the temperature of the cylinder head with an external temperature gauge.
- Check that the diagnostic tool reading is within 10°C of the measured temperature with warm and cold engine. Be sure the reading is stable and not fluctuating a number of degrees.
If the reading is stable and does not fluctuate a number of degrees, the fault has been rectified. Clear DTCs from all systems.
Courtesy of SAAB-SCANIA OF AMERICA, INC.
Courtesy of SAAB-SCANIA OF AMERICA, INC.
Courtesy of SAAB-SCANIA OF AMERICA, INC.