ECM Code EO23 - Est Circuit Problem (2 Of 2)
The distributor reference ground (circuit No. 453) is a common ground between the ECM and HEI module. The ECM and HEI compare by-pass, EST, and reference voltages to ground voltage on circuit No. 453. An open circuit No 453 to the HEI or ECM can cause a failure of the ECM to recognize a reference pulse or the HEI 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 EO23. If ECM has by-pass at 5 volts, the module should accept EST information, and EST voltage should be high (.5-2.8 volts). If by-pass is at zero volts, module should ground EST circuit and the EST voltage should be low (less than .5 volts). Possible causes of code EO23 are:
- Circuit No. 423 (EST) open or grounded.
- Circuit No. 424 (by-pass) open or grounded.
- Circuit No. 453 (reference ground) open to ground at HEI module or ECM.
- ECM has poor connection to engine through circuit No. 450 (ground).
- ECM or HEI module faulty.NOTE: Test numbers refer to test numbers on diagnostic chart.
- 5) This step checks HEI module's ability to recognize a voltage on by-pass circuit and to top grounding EST (ECM controlled timing).
- 6) This step checks for by-pass signal to module. If by-pass signal is being sent by ECM to HEI, and if module is interpreting by-pass voltage correctly, then module will switch off ground to EST.
- 7) If chart leads to "EST CIRCUIT IS OK", then a fault may exist in the 4-way connector. Check connector and terminals for damage. If connector is okay, plug in connector and retest for code EO23.