DTC 43

Code 43 - Electronic Spark Control (ESC) Circuit:

Wiring Diagram for Electronic Spark Control (ESC) Circuit:

CODE 43 - ELECTRONIC SPARK CONTROL (ESC) CIRCUIT

Circuit Description:


The Electronic Spark Control (ESC) system is comprised of a knock sensor and an ESC module.

The ESC module sends a voltage signal (8 to 10 volts) to the Electronic Control Module (ECM).

When the sensor detects detonation, the module turns "OFF" the circuit to the ECM and the voltage at ECM terminal "B7" drops to 0 volts. The ECM then retards EST as much as 20 degrees in one (1) degree increments to reduce detonation. This happens fast and frequently enough that if looking at this signal with a DVM, you won't see 0 volt, but an average voltage somewhat less than what is normal with no detonation.

A loss of the knock sensor signal or a loss of ground at the ESC module would cause the signal at the ECM to remain high. The ECM would control ignition timing (EST) as if no detonation were occuring. The EST would not be retarded, and detonation could become severe enough under heavy engine load conditions to result in pre-ignition and potential engine damage.

Loss of the ESC signal to the ECM would cause the ECM to constantly retard the EST to its max retard of 20 degrees. This could result in sluggish performance and cause a Code 43 to set.

Code 43 will set when:

^ Engine running

^ ESC input signal has been low more than 2.2 seconds


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. If the ECM data (knock signal) display is fluctuating widely, the ECM is monitoring a low voltage signal on circuit (457) at ECM terminal "B7".

2. Probing ESC harness terminal "C" with a test light connected to 12 volts should result in the "OLD PA3" (knock signal) display holding a steady reading due to over 8 volts having been applied to ECM terminal "B7" through CKT 457.

3. If over 6 volts is measured at ECM terminal "B7", CKT 457 is OK and the fault is due to a poor connection at the ECM or the ECM is faulty.


Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

^ Poor Connection or Damaged Harness - Inspect ECM harness connectors for backed out terminal "B7", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

^ Intermittent Test - If connections and harness checks out OK, "Scan" knock signal (OLD PA3) while moving related connectors and wiring harness. If the failure is induced, the knock signal display will change. This may help to isolate the location of the malfunction.