Pcm Code E023, Est Circuit Problem: Action

PCM turns on SERVICE ENGINE SOON light and will not enable spark timing control. Engine will start and run on base timing.

1. When circuit No. 423 is shorted to ground, engine will have a long crank and hard start condition. When PCM detects grounded circuit, by-pass line will be shifted low.
2. With only distributor reference (distributor reference ground jumpered), engine will run on back-up spark control. This checks for proper ground connections between PCM and engine and between PCM and HEI.
3. This ensures PCM provides EST output signal over circuit No. 423.
4. This checks if HEI module can ground EST signal with an open by-pass circuit.
   NOTE: Test numbers refer to numbers on diagnostic chart.
5. This checks if HEI module can recognize a voltage on by-pass circuit and stop grounding EST (PCM-controlled timing).
6. This checks for by-pass signal to module. If by-pass signal is being sent by PCM to HEI and if module is interpreting by-pass voltage correctly, module will switch off ground to EST.
7. Fault may exist in 6-way connector. Check connector and terminals for damage. If connector is okay, plug in connector, and retest for PCM Code E023.

Fig 1: PCM Code E023, Schematic, EST Circuit Problem

Courtesy of GENERAL MOTORS CORP.

Fig 2: PCM Code E023, Flow Chart, EST Circuit Problem (1 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 3: PCM Code E023 (1 Of 2)

Fig 4: PCM Code E023, Flow Chart, EST Circuit Problem (2 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 5: PCM Code E023 (2 Of 2)