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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 14303
Experience:  Have owned a repair shop for 25 yrs.
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SUBURBAN 1500: I HAVE A 1993 CHEV...neer the throtle BODY AND SHOWS A

Customer Question

Submitted: 6 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 6 years ago.


you can get this code from the knock sensor or if it needs a tune up also..the electronic spark control module is on the fire wall..or it may be behind the glove box near the computer.or on the right side of the engine on the bracket that has the egr solinoid on it,,.please print and use the code chart below to help you fix this code


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Description and Operation


ESC Wiring Diagram

A knock sensor is mounted on the engine block. It is connected by a blue wire to the ESC module, mounted on a bracket on the back of the engine. The knock sensor, in response to engine knock (detonation), sends a signal to this module. The module decodes these signals, and if they indicate spark knock type noise, a retard signal is sent to the ECM which in turn retards the spark advance.


The Electronic Spark Control (ESC) system is designed to retard the spark timing up to 20~ to reduce spark knock (detonation) in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

Varying octane levels in todays gasoline can cause detonation in an engine. Detonation is called spark knock.


The ESC system has three components:


  • ESC Module
  • ESC Knock Sensor
  • ECM

The ESC knock sensor detects abnormal vibrations (spark knocking) in the engine. The sensor is mounted in the engine block near the cylinders. The ESC module receives the knock sensor information and sends a signal to the ECM. The ECM then adjusts the Electronic Spark Timing (EST) to reduce the spark knocking.

The ESC module sends a voltage signal (8 to 10 volts) to the ECM when no spark knocking is detected by the ESC knock sensor, and the ECM provides normal spark advance.

When the knock sensor detects spark knock, the module turns OFF the circuit to the ECM. The ECM then retards EST to reduce spark knock.

Powertrain Controls - ECM/PCM


Code 43 - Electronic Spark Control (ESC) Circuit
Wiring Diagram For Code 43 - Electronic Spark Control (ESC) Circuit



Circuit Description :

Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the ECM to retard timing. The ECM will retard the timing when knock is detected and rpm is above about 900 rpm.

Code 43 means the ECM has been low voltage at CKT 485 terminal "B7" for longer than 5 seconds with the engine running or the system has failed the functional check.

This system performs a functional check once per start-up to check the ESC system. To perform this test, the ECM will advance the spark when coolant is above 95~C and at a high load condition (near W.O.T.). The ECM then checks the signal at "B7" to see if a knock is detected. The functional check is performed once per start-up and if knock is detected when coolant is below 95~C (194~F), the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light will remain "ON" until ignition is turned "OFF" or until a knock signal is detected.

Test Description : Numbers below refer to circled numbers on the diagnostic chart.
  1. If the conditions for a Code 43 are present, the "Scan" will always display "YES." There should not be a knock at idle unless an internal engine problem, or a system problem exists.
  2. This test will determine if the system is functioning at this time. Usually a knock signal can be generated by tapping on the right exhaust manifold. If no knock signal is generated, try tapping on block close to the area of the sensor.
  3. Because Code 43 sets when the signal voltage on CKT 485 remains low, this test should cause the signal on CKT 485 to go high, The 12 volts signal should be seen by the ECM as "no knock" if the ECM and wiring are OK.
  4. This test will determine if the knock signal is being detected on CKT 496 or if the ESC module is at fault.
  5. If CKT 496 is routed to close to secondary ignition wires, the ESC module may see the interference as a knock signal.
  6. This checks the ground circuit to the module. An open ground will cause the voltage on CKT 485 to be about 12 volts which would cause the Code 43 functional test to fail.
  7. Connecting CKT 496 with a test light to 12 volts should generate a knock signal. This will determine if the ESC module is operating correctly.
Diagnostic Aids :

Code 43 can be caused by a faulty connection at the knock sensor at the ESC module or at the ECM, Also check CKT 485 for possible open or short to ground.

See Diagnosis By Symptoms - No Trouble Codes Stored.

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