E038

ECM Code E038:

DFI Sensor Circuit:

DESCRIPTION:

The MAT sensor is a thermistor or variable resistor that varies in resistance with temperature. The MAT sensor is a two wire sensor with a reference or signal voltage coming from the ECM to sensor pin B, CKT 472 and a reference ground on pin A, CKT 476. As the temperature of the sensor decreases, sensor resistance increases.

The signal voltage from the ECM to pin B increases as sensor temperature decreases because less current flows from sensor pin B through the sensor element to ground (more of the signal voltage is dropped across the sensor element). Low temperature means high signal voltage on CKT 472 and high temperature means low signal voltage on CKT 472.

Code E038, open MAT sensor, sets because the ECM assumes that the manifold air temperature can't be -35 to -40°C with a coolant temp of -5°C or greater.

TEST CONDITIONS:

1. Codes E014 and E015 clear.
2. Coolant sensor greater than or equal to -5°C.

FAILURE CONDITIONS:

MAT sensor value less than -35°C.

ACTION TAKEN:

1. ECM illuminates "SERVICE ENGINE SOON" telltale.
2. ECM commands BCM to display "SERVICE SOON" message on CCDIC.
3. ECM turns off both air management solenoids.
4. ECM uses 40°C for a MAT value when coolant temp is greater than 40°C.
5. ECM substitutes coolant temp for MAT when coolant temp is less than 40°C.

NOTES ON FAULT TREE:

1. If the sensor is open, ECM parameter ED05 should read -35°C or less. If not, then sensor signal is not open at this time, see NOTE ON INTERMITTENTS.

2. Checking ECM and sensor circuitry from ECM to sensor connector. If ECM parameter ED05 reads 142°C to 151°C with connector pin A shorted to pin B then the sensor circuits and ECM are OK.

3. Checking for open sensor ground.

4. Checking for ECM's ability to recognize a short to ground on MAT input.

5. Fault is most likely at the ECM connector of ECM. Before replacing the ECM, perform the "ECM Replacement Check", CHART C-1.

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

NOTE ON INTERMITTENTS:

Manipulate CKT 472 and 476 wiring, the MAT connector and ECM connector while observing ECM parameter ED05. If the failure is induced, the MAT will jump from its normal value to the open signal circuit reading of -35 to -40°C. If wiring and connectors check out OK, substitute a known good MAT sensor and retest.

Review the snapshot data parameters stored with this code to verify failure condition. If the failure condition is verified, check and repair intermittent wiring connection, or sensor.