No Start / No Spark with Code 12 (RPM Signal) - Bad ECU Replacement

1988 7M-GE Supra that previously ran and drove fine would not start after sitting for a couple of days. OBD1 code 12 (RPM signal failure) was stored. No spark present. Distributor had already been replaced and wiring checked with no improvement.

The ECU (Engine Control Unit) had failed internally. While Code 12 commonly points to the CPS (Crank Position Sensor) or its wiring, in this case the CPS circuit within the ECU itself was faulty. The ECU was still functional enough to generate the code but could not properly process the RPM signal from the CPS.

Moderate confidence — Original poster confirmed this resolved the issue