Intake Air Heater: Testing and Inspection
To perform a complete test of this sensor and its circuitry, refer to Powertrain Management/Computers and Controls/Testing and Inspection. To test the sensor only, refer to following:Air Temperature Sensor:
1. Disconnect wire harness connector from intake manifold air temperature sensor. The sensor is located on top of intake manifold and to rear of air heater.
Sensor Resistance:
2. Test resistance of sensor with an input impedance (digital) volt-ohmmeter. The resistance (as measured across sensor terminals) should be as shown in the SENSOR RESISTANCE (OHMS)-INTAKE MANIFOLD AIR TEMPERATURE chart. Replace sensor if it is not within range of resistance specified in chart.
3. Test resistance of wire harness. Do this between powertrain control module (PCM) wire harness connector terminal A-15 and sensor connector terminal. Also check between PCM terminal AM (sensor return) to sensor connector terminal. Repair wire harness as necessary if resistance is greater than 1 ohm.
INTAKE MANIFOLD AIR HEATER TEST
The intake manifold air heater is controlled by the powertrain control module (PCM) through the intake manifold air heater relays (Fig. 19). This is done after a specified signal is sent to the PCM from the intake manifold air temperature sensor. Two heating elements are located within the air heater assembly. A separate heavy-duty cable is connected to a separate terminal to supply power for each element.
PREHEAT/POST-HEAT CYCLE
Refer to Description and Operation for preheat/post heat cycle information. The PCM provides a ground path for the intake manifold air heater relays. The ground path is provided if intake manifold air temperature is below 15-19°C (59-66°F) when the ignition key is initially placed in the ON position. When the ground is provided, the air heater is energized to start the preheat cycle. The preheat-cycle can be tested with a voltmeter or test light. If the intake manifold air temperature is above 15°C (59°F), the wait-to-start warning lamp will not illuminate and the air heater will not be energized.
1. With the engine not running, and intake manifold air temperature below 15-19°C (59-66°F), turn the ignition key to the ON position.
2. The wait-to-start warning lamp will come on and the air heater relays should click ON signaling the start of the preheat cycle. If the engine starter is engaged before the preheat cycle of the heaters is complete, the PCM will stop the remaining preheat cycle.
3. Check for battery voltage at both air heater terminals. The heater will only be energized for 10 to 30 seconds. Refer to the Air Heater Cycle Chart for a time/temperature comparison.
HEATER TEST
1. Disconnect both negative battery cables at both batteries.
2. Lift the rubber shields from each of the cable connectors at the intake manifold air heater to expose the cable terminals. Do not disconnect cable nuts.
3. Use an ohmmeter to test the resistance between the cable terminal (not the mounting stud) and a ground. The resistance should be zero (0). If not inspect for corroded or dirty cable connections. Clean or repair the connections and retest before replacing heater. If resistance is now anything other than zero (0), proceed to next step.
4. Disconnect both cables from the intake manifold heater (two nuts).
5. Measure the resistance from each of the air heater terminal threaded studs to a ground. The resistance should be zero (0). If the ohmmeter is still reading anything other than zero (0), replace the intake manifold air heater elements. The heater elements are part of the intake manifold and will require manifold replacement.
6. After testing and repairing, connect battery cables to both batteries.