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
Normal pattern (0-12
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
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.