P1708

What Does Code P1708 Mean?

DTC P1708 signifies an electrical malfunction within the Clutch Pedal Position (CPP) switch circuit. The Powertrain Control Module (PCM), or Engine Control Module (ECM) in some vehicle architectures, continuously monitors the voltage signals from the CPP switch to determine the clutch pedal’s position. This switch serves multiple critical functions, including acting as a neutral safety switch to prevent engine cranking when the clutch is not depressed, disengaging cruise control, and sometimes informing the engine management system of load changes during manual gear shifts. When the PCM detects a signal from the CPP switch circuit that is outside of the expected voltage range, indicates an open circuit, a short to ground, or a short to voltage, or if the signals from redundant CPP switches (if applicable) do not correlate as programmed, it interprets this as a malfunction and sets code P1708.

Common Symptoms

• Engine Fails to Crank or Start: This is the most prevalent symptom, as the CPP switch typically acts as a neutral safety interlock.
• Cruise Control Malfunction: Inability to engage cruise control, or unexpected disengagement while driving.
• Intermittent Starting Issues: The engine may crank only sporadically, even when the clutch pedal is depressed.
• Check Engine Light (CEL) Illumination: The Malfunction Indicator Lamp (MIL) will be illuminated on the dashboard.
• Abnormal Engine Behavior (Rare): In some advanced manual transmission systems, an incorrect clutch signal might mildly affect idle stability or engine response during gear changes, although this is less common for a direct circuit malfunction.

What Causes the Code P1708?

• Faulty Clutch Pedal Position (CPP) Switch: Internal mechanical failure of the switch mechanism, degradation of electrical contacts, or complete electrical sensor failure.
• Wiring Harness Issues: An open circuit (broken wire), short circuit to ground, short circuit to voltage, or excessively high resistance within the CPP switch wiring harness. This also includes corroded or loose electrical connectors.
• Misadjusted Clutch Pedal Position Switch: The switch may be physically mounted incorrectly or be out of adjustment, preventing it from accurately sensing the clutch pedal’s full range of motion or detecting the correct resting position.
• Faulty Powertrain Control Module (PCM/ECM): While less common, an internal fault within the PCM preventing it from correctly processing the CPP switch input signal is a possibility.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is crucial for P1708:

1. Visual Inspection: Begin by visually inspecting the clutch pedal area. Examine the CPP switch for any physical damage, ensuring it is securely mounted and that its plunger or arm makes proper contact with the clutch pedal arm throughout its travel. Check the electrical connector for corrosion, pushed-out pins, or damage. Follow the wiring harness from the switch as far as possible, looking for chafing, cuts, or signs of rodent damage.
2. OBD-II Scanner Live Data: Connect an OBD-II diagnostic scanner and navigate to the live data stream. Locate parameters related to “Clutch Pedal Position Switch” (or similar terminology like “Clutch P/P Switch”). Observe the reported state (e.g., ON/OFF, Engaged/Disengaged, or a varying voltage) while manually depressing and releasing the clutch pedal. The switch state should change reliably and consistently without flickering or sticking.
3. Digital Multimeter (DMM) Testing – Switch Functionality:
   • Disconnect the electrical connector from the CPP switch.
   • Using a DMM set to continuity or resistance mode, test the terminals of the switch itself.
   • With the clutch pedal in its fully released position, note the DMM reading.
   • Manually depress the clutch pedal fully and note the DMM reading again.
   • The switch should reliably transition between an open circuit (infinite resistance) and a closed circuit (near zero resistance), or vice-versa, depending on whether it’s a normally open or normally closed switch. Compare readings to the vehicle’s specific service manual specifications.
4. DMM Testing – Circuit Integrity:
   • With the ignition ON and the CPP switch still disconnected, use the DMM to check for the presence of reference voltage (typically 5V or 12V, depending on the system design) and a solid ground at the terminals of the vehicle-side connector that leads to the PCM. This verifies power and ground supply to the switch circuit.
   • With the ignition OFF and the PCM connector potentially disconnected (consult service manual for pinouts), check for excessive resistance or an open circuit in the individual wires between the CPP switch connector and the PCM connector. This identifies breaks or high-resistance points in the wiring.
   • Check for any shorts to ground or shorts to battery voltage in the signal wire.
5. Adjustment Verification: If the CPP switch is of an adjustable type, verify that its engagement point with the clutch pedal arm is set correctly according to the manufacturer’s specifications. Some switches are self-adjusting upon installation, but physical damage or incorrect initial installation can lead to maladjustment.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace the Clutch Pedal Position Switch: This is the most frequent solution for P1708. If DMM testing confirms the switch is internally faulty, replace it with a new, high-quality OEM or reputable aftermarket unit. Ensure the new switch is correctly installed and, if applicable, properly adjusted.
• Repair or Replace Wiring Harness Components: If diagnostic testing reveals an open circuit, short, or high resistance in the wiring harness or a corroded/damaged connector, the affected section should be meticulously repaired or replaced. Use proper automotive-grade wiring repair techniques, including soldering, heat-shrinking, and ensuring good electrical contact at all terminals.
• Adjust the CPP Switch: If the existing switch is found to be functional but simply out of adjustment, carefully follow the vehicle manufacturer’s procedure to correctly adjust its position relative to the clutch pedal arm. This often involves specific clearances or a self-setting procedure during installation.
• PCM Replacement (Rare): Only after all other potential causes (switch, wiring, adjustment) have been thoroughly inspected, tested, and ruled out should the PCM be considered as the culprit. PCM replacement typically requires programming and is a costly repair.

Mechanic’s Tip: When installing a new CPP switch, particularly a self-adjusting type, ensure the clutch pedal is fully depressed or in its furthest rearward position (as specified by the manufacturer) before snapping the switch into place. This allows the switch’s internal plunger mechanism to extend fully and set its proper resting position against the pedal arm upon release. Always clear DTCs and verify proper operation of engine cranking and cruise control after any repair.