P06D4: Reference E high uses the VSS2 rail’s own voltage scale

P06D4 identifies a high condition on sensor reference voltage E. GM’s TCM row maps that label to VSS2, the second speed-sensor supply. The documented circuit should not be confused with a nominal five-volt reference simply because both use the word “reference.”

A high limit with a wider hysteresis

The monitor compares VSS2 with a boundary above 10.5 volts. It uses 500 millivolts of hysteresis and at least 75 milliseconds of confirmation. These values differ from the low-side VSS2 check, so copying a neighboring code’s hysteresis would change the test.

The main battery range is separately constrained to above 8.75 and below 18 volts. Cranking, the STOP key state and active P0882/P0883 conditions prevent the ordinary assessment.

Retain rail-specific evidence

A useful record distinguishes VSS2 voltage from VSS1, the five-volt references and battery voltage. Those readings may all be available in the same diagnostic session but do not answer the same question.

The summary supplies no connector pinout and does not identify whether a connected branch or internal supply path caused the high reading. Use the matching circuit information to localize the fault. A cleared code or a healthy different reference rail cannot independently prove that VSS2 has returned to normal. Verification needs the applicable monitor to run with the correct supply conditions.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 909.