Action Taken
- PCM turns on "Service Engine Soon" telltale.
- PCM substitutes 40°C for MAT when coolant temperature 40°C or greater
- PCM substitutes coolant temp for MAT when coolant temp is 40°C.
NOTE:
The following step numbers refer to circled numbers on diagnostic chart. See Fig 1
. For circuit identification, see Figure
.
- If the MAT sensor is open, PCM data ED05 should read -35°C or less. If not, then the sensor signal is not open at this time, see Notes On Intermittents .
- Checking PCM and sensor circuitry from PCM to sensor connector. If PCM Data ED05 reads 148-151°C with connector Pin A shorted to Pin B, then the sensor circuit and PCM are OK.
- Checking for an open sensor ground.
- Checking PCM's ability to recognize short to ground on MAT input.
- Fault is most likely at PCM connector or PCM. Before PCM is replaced, perform PFI CHART C-1: PCM REPLACEMENT CHECK .
- The MAT 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 MAT sensor replacements, check for signs of backfire or high intake manifold air temperature due to improper valve train operation.