Problem: Vehicle came in with the MIL “On” and no perceivable drivability issues.
Details: The technician connected a scan tool and retrieved DTC P2527 (EGR valve signal circuit open). He checked for battery voltage at the EGR valve on the black/dark green wire (pin #2) and the ground on the brown wire (pin #3) using a sealed beam headlamp. The circuit test results were good. Next, he scope-checked the signal (gray) wire at the PCM (pin 71) while activating EGR valve with a scan tool. NOTE: The pattern range for a good circuit should be from 0-12 volts. If the circuit is open, the pattern will range from 0-4 volts. In this case, the signal circuit pattern was between 0-4 volts (see pattern samples below).
Bad waveform pattern (0-4 volts)
Normal pattern (0-12 volts)
Confirmed Repair: The technician found a break in the gray signal wire. He repaired the wire, cleared the code, then performed a drive cycle to run the monitors. The problem was repaired.
Diagnostic Insight: You may wonder how this ignition signal wire failure could have caused this problem. The DDM senses the ignition status on that yellow wire and sends that information through the network data line to the mirrors, sunroof and windows. If the ignition signal is lost to the DDM, as in this case, it can’t communicate that information to the other modules in its network and those accessories don’t operate.