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Throttle Position Sensor (APPS) Circuitry

The purpose of this document is to detail the Accelerator Pedal Position Sensor (APPS) circuit layout and provide a comprehensive pinout for diagnostic tracing. This guide identifies common failure points and connection junctions between the pedal and the Engine Control Module (ECM).

Tools Required

  • Digital Multimeter (DMM)

  • Pin Projection/Terminal Tension Gauges (to check for spread terminals)

  • Contact Cleaner and Dielectric Grease

  • Torque Wrench (for battery cable verification)

Vehicle Preparation

  1. Safety: Ensure the vehicle is parked, wheels chocked, and the ignition is in the OFF position before disconnecting any ECM or chassis connectors.

  2. Schematic Reference: If the vehicle is a Dual Drive configuration, you must refer to Schematic 080A-0609 for additional harness routing.

Part 1: Circuit Path and Pinout Matrix

The APPS signal travels through five primary connection points. Use the table below to perform continuity and resistance checks across the harness.

Wire Number APPS Cavity Extension Harness (1 or 2) 102-Pin Floor Pass-Through 35-Pin Chassis/ECM 96-Pin ECM Connector
Wire 002 C C (Conn 1) 67 2 9
Wire 003 A B (Conn 1) 68 3 10
Wire 004 B A (Conn 1) 73 4 33
Wire 008 D C (Conn 2) 93 6 8
Wire 009 E B (Conn 2) 76 5 61
Wire 010 F A (Conn 2) 94 12 64

Part 2: Sequential Connector Locations

  1. APPS: 6-pin connector directly at the pedal.

  2. APPS Extension: Two 3-pin connectors at the end of the pedal harness.

  3. Floor Connector: 102-pin pass-through.

  4. Chassis-to-ECM: 35-pin connector located between the frame and the left side of the transmission.

  5. ECM: 96-pin main engine controller interface.

Common Issues and Diagnosis

1. Corrosion at the 35-Pin Connector Located near the transmission, this connector is a high-traffic area for moisture and road salt.

  • Symptom: High resistance or open circuit fault codes.

  • Action: Inspect pins for green corrosion or moisture intrusion. Clean and apply dielectric grease.

2. Terminal Tension (Spread Pins) Forceful pulling on the APPS extension harness can "spread" the female terminals at the 6-pin pedal connector.

  • Symptom: Intermittent "dead pedal" or erratic signal codes.

  • Action: Use a terminal tension tool to verify a tight fit. Replace the connector shell/terminals if tension is lost.

3. System-Wide Voltage Stability The APPS is highly sensitive to voltage "noise." Loose battery or ground cables are the primary culprit for ghost codes.

  • Checkpoints:

    • Batteries, Alternator, and Starter terminals.

    • Cab pass-through studs (interior and exterior).

    • Main Cab Power Solenoid (behind interior fuse panel).

    • Crucial: Check the Orange and Red battery cables on the rear of the in-cab fuse panel.