Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 43:

Knock Sensor Circuit:

CIRCUIT DESCRIPTION
The Knock Sensor (KS) system is used to detect engine detonation. The Powertrain Control Module (PCM) will retard the spark timing based on signals from the KS module. The knock sensors produce an Alternating Current (AC) voltage which is sent to the KS module. The amount of AC voltage produced by the sensors is determined by the amount of knock. The circuitry within each KS causes the PCM's 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 1.5 volts.

The internal PCM test run on the KS circuit will determine if it is operating correctly.

DIAGNOSTIC TROUBLE CODE (DTC) 43 WILL SET WHEN
If the PCM detects that any of the following voltage conditions have been met for 5 seconds, DTC 43 will be set: One sensor being open - voltage between about 2.2 volts and 4.1 volts, both knock sensors being open - voltage greater than 4.1 volts, or both knock sensors being grounded - voltage less then 0.78 volt.

ACTION TAKEN (PCM DEFAULT)
The Malfunction Indicator Lamp (MIL) will illuminate. The PCM will retard timing to a predetermined maximum based on current RPM and MAP. Some loss of performance may result.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. If an audible knock is heard from the engine, repair the internal engine problem, as normally no knock should be detected at idle.

The PCM supplies 5 volts on CKT 496 which should be present at the knock sensor terminals when the sensors are disconnected.

2. This test determines if the knock sensor is faulty or if the KS module is faulty.

3. CKT 496 shorted to voltage will set DTC 43 and indicate on Tech 1 scanner as both sensors open. With both sensors and the PCM disconnected, no voltage should be present on CKT 496.

4. An improperly installed knock sensor can prevent the knock sensor from grounding to the block.

5. If a short to battery voltage is found, additional component damage may have occurred. If DTC 43 resets after repairing the short, it will be necessary to re-run this chart to locate any additional faults.

DIAGNOSTIC AIDS
The PCM has the ability to diagnose opens and shorts in the KS circuit. The Tech 1 scanner will display if one or both sensor are open or if both are grounded when the PCM detects these conditions.

Check CKT 496 for a potential open or short to ground.

Also, check for proper installation of the KS module.

KS sensor wires routed too closely to secondary ignition components may be susceptible to Electromagnetic Interference (EMI).

Refer to Diagnosis By Symptom/Intermittents. - Intermittent Malfunctions