P038

DTC P038:

Sensor Circuit:

DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor, or variable resistor, that varies resistance based on temperature. High temperature will result in low signal voltage. Code P038 sets when the Powertrain Control Module (PCM) sees low voltage signal when coolant is -5°C or greater.

TEST CONDITIONS
1. Codes P014 and P015 not set.
2. Engine coolant temperature -5°C or greater.
OR
3. If engine coolant temperature at key on is -25°C or less the engine must be run for 15 minutes before Code P038 will be tested for.

FAILURE CONDITIONS
IAT -37°C or less.

ACTION TAKEN
1. PCM turns "ON" the "Service Engine Soon" Malfunction Indicator Lamp (MIL).
2. PCM substitutes 40°C for IAT when engine coolant temperature is 40°C greater.
3. PCM substitutes engine coolant temperature for IAT when engine coolant temperature is less than 40°C.

NOTES ON FAULT TREE
1. If the IAT sensor is open, PCM data PD05 should read -37°C or less. If not, then the sensor signal is not open at this time, refer to "NOTES ON INTERMITTENTS."

2. Checking PCM and sensor circuitry from PCM to sensor connector. If PCM Data PD05 reads 148°C-151°C with connector pin "A" shorted to pin "B," then the sensor circuit and PCM are OK.

3. Checking for an open sensor ground.

4. Checking PCM's ability to recognize short to ground on IAT input.

5. Fault is most likely at PCM connector or PCM. Before PCM is replaced, check for damaged pins or poor connection.

6. The IAT sensor can be damaged by backfire in the intake manifold and by excessive intake heat due to valve train faults. If the vehicle has had multiple IAT sensor replacements, check for signs of backfire or high intake manifold air temperature due to improper valve train operation.

NOTES ON INTERMITTENTS
Manipulate CKT 472 and 452 wiring, IAT sensor connector, and PCM connector while observing PCM Data PD05. If the failure is induced, the data value will jump from its normal value to the open circuit reading of -35° to -40°C. Disconnect and reconnect both the IAT sensor and PCM connectors and ensure that they are latched. If wiring and connectors check out OK, substitute a known good IAT sensor and retest.