DTC 43

*** UPDATED BY TSB 416516, DATED AUGUST, 1994

Code 43 Chart.:

Knock Sensor.:

CIRCUIT DESCRIPTION
The knock sensor system is used to detect engine detonation. The Powertrain Control Module (PCM) will retard the spark timing based on signals from the Knock Sensor (KS) module. The knock sensor(s) produces an AC voltage which is sent to the KS module. The amount of AC voltage produced by the sensor(s) is determined by the amount of knock. The circuitry within each knock sensor causes the PCM's 5 volts to be pulled down so that under a no knock condition, CKT 496 would measure about 2.5 volts.
The internal PCM test run on the KS circuit will determine if it is operating correctly.

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 of two sensors being open - voltage between about 2.2 volts and 4.1 volts, one sensor being open - voltage greater than 4.1 volts, or sensor(s) grounded - voltage less than 0.78 volt.

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

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) 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 terminal(s) when the sensor(s) is disconnected.
2. This test determines if the knock sensor(s) is faulty or if the KS module is faulty.
3. CKT 496 shorted to voltage will set DTC 43 and indicate on a Tech 1 (or equivalent Scan tool) as the sensor(s) open. With the sensor(s) and the PCM disconnected, no voltage should be present on CKT 496.
4. An improperly installed knock sensor(s) can prevent the knock sensor(s) 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 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 (or equivalent Scan tool) will display if one or both sensors 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 Electro Magnetic Interference (EMI) interference.

Refer to Diagnosis By Symptom / Intermittents. Testing and Inspection