C 2500 Suburban 2WD V8-6.5L DSL Turbo VIN F (1995)
Accelerator Pedal Position Sensor: Testing and Inspection
Accelerator Pedal Position (APP) Module
Accelerator Pedal Position (APP) Sensor
If the Powertrain Control Module (PCM) has determined that there is a fault in one Accelerator Pedal Position (APP) sensor the PCM will store a
current and history Diagnostic Trouble Code (DTC) but, it will not turn on the "Service Throttle Soon" lamp. The vehicle and throttle pedal will operate
normally if only one of the three APP sensors is at fault. If the PCM has determined two APP sensors are faulty, a current and history DTC will set and
the PCM will turn on the "Service Throttle Soon" lamp. At this point, some engine performance will be lost. If three APP sensors malfunction, a current
and history DTC will be stored, the "Service Throttle Soon" lamp will come "ON," and the PCM will only allow the vehicle to idle. If the PCM has
recognized an intermittent fault (a fault not recognized by the normal APP DTC setting criteria), it will then only allow the vehicle to operate under
limited performance and store a DTC 84.
A scan tool reads APP 1 position in voltage, and should read about 0.50 volt while the engine is idling. Voltage should increase at a steady rate as
accelerator pedal is moved to Wide Open Throttle (WOT). APP 2 position is also read in voltage, and should read about 4.5 volts at idle, and should
steadily decrease to a about 1.5 volts as accelerator pedal is moved to WOT. APP 3 is also read in voltage, and should read about 4.0 volts at idle, and
should steadily decrease to about 2.0 volts. Its possible idle voltage may vary, because the PCM has a "learning" ability which allows it to make
corrections for minor variations.
