Code E23: Est Circuit Problem (2 Of 2)

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

The distributor reference ground circuit No. 453 is a common ground between ECM and HEI. The ECM and HEI compare by-pass, EST and reference voltages to ground voltage on circuit No. 453. Circuit No. 453 open to HEI or ECM can cause a failure of ECM to recognize a reference pulse or failure of module to recognize an EST pulse.

The ECM compares status of EST circuit to status of by-pass circuit in order to detect a fault and set Code E23. If ECM has by-pass at 5 volts, module should accept EST information. EST voltage should be high (.5-2.8 volts). If by-pass is zero volts, module should ground EST circuit and EST voltage should be low (less than .5 volt).

Possible causes of Code E23 are:

Circuit No. 423 (EST) open/ground.
Circuit No. 424 (by-pass) open/ground.
Circuit No. 453 (reference ground) open to ground at HEI or ECM.
ECM with a poor connection to engine through circuit No. 450 grounds.
ECM or HEI module faults.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 5) Checks for HEI module ability to recognize a voltage on by-pass circuit and to stop grounding EST (ECM controlling timing).

Test Number 6) Checks for by-pass signal to module. If by-pass is being sent by ECM to HEI, and if module is interpreting by-pass voltage correctly, the module will switch off the ground to EST.

Test Number 7) If chart leads to EST circuit and circuit is okay, a fault may exist in 6-way weatherpack. Check for proper connector mating and for pins backing out of weatherpack. If connector is okay, reconnect 6-way, clear codes and retest.

Fig 1: Code E23: Circuit Diagram (2 of 2)

Fig 2: Code E23: Flow Chart (2 of 2)