DTC 131

DTC 131 Chart:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The knock sensor is used to detect engine detonation and allow the Powertrain Control Module (PCM) to retard the Ignition Control (IC) timing based on the signal being received. The circuitry within the knock sensor causes the PCM's supplied 5 volt signal to be pulled down, so that under a no knock condition CKT 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts DC voltage. The amplitude and signal frequency are dependent upon the knock level.
The PCM tests the ability of the knock sensor to detect detonation by advancing the spark timing to a point which should cause detonation to occur. If the PCM does not detect a signal indicating detonation from the knock sensor, DTC 131 will be set.
The PCM will run the DTC 131 test when the following conditions are met:

- MAP value steady.
- IAT value greater than 30°C (86°F)
- Engine coolant temperature 151°C (304°F) or greater.
- Engine speed between 1200 and 1900 RPM.
- Knock retard at 0°.

When the above conditions are met, the PCM tests the knock sensor by incrementing the spark advance until knock is detected or until a maximum value which varies according to coolant temperature is reached.

DTC 131 WILL SET WHEN
- Spark advance is greater than an amount which should cause detonation to be detected. (This varies with coolant temperature.)
- Detonation is not detected within 1 second.

ACTION TAKEN (PCM WILL DEFAULT TO)
With DTC 131 set, the PCM will alter fuel delivery and spark timing under high load conditions to reduce the chance of detonation occurring. DTC 131 does not illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).

DTC 131 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Check the knock sensor ability to detect an induced knock.
2. Determines if the fault is a circuit or a sensor problem.

DIAGNOSTIC AIDS
Check CKT 496 for an intermittent open or short to ground. Also check for proper installation of PROM.
Refer to Detonation, Spark Knock in Diagnosis by Symptom. Detonation/Spark Knock/Pings
If DTC 36 is current, refer to that DTC first.