E038

Diagnostic Chart.:

Sensor Circuit:

DESCRIPTION:

The MAT sensor is a thermistor or variable resistor that varies in resistance with temperature. High temperature means low signal voltage. Code E38 sets when the ECM sees low voltage signal when coolant is -5°C or greater.

TEST CONDITIONS:

1. Codes E14 and E15 not set.
2. Coolant temperature -5°C or greater.

FAILURE CONDITIONS:

MAT sensor value less than -37°C.

ACTION TAKEN:

1. ECM illuminates "SERVICE ENGINE SOON" telltale.
2. ECM uses 40°C for MAT value when coolant temp is greater than 40°C.
3. 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 P.0.5 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 P.0.5 reads 148°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.

6. MAT sensor can be damaged by backfire in the intake manifold or by excessive intake manifold 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 469 wiring, the MAT connector and ECM connector while observing ECM parameter P.0.5. 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.