Diagnostic Aids

1995 GMC Suburban K2500, 7.4 NSECTION Diagnostic Aids

With ignition on and engine off, EGR pressure is equal to atmospheric pressure with signal voltage being high. This information is used by PCM as an indication of vehicle altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same plus or minus .4 volt. An intermittent open in the EGR control pressure/BARO signal circuit or the 5-volt reference circuit will cause DTC 31 to set.

Fig 1: DTC 31 Schematic (6.5L Diesel) EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)
G95J26939
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.