P1694

What Does Code P1694 Mean?

The OBD-II diagnostic trouble code P1694 signifies a malfunction within the electrical circuit controlling the turbocharger/supercharger charge air relief valve. This circuit is critical for managing boost pressure, primarily to prevent compressor surge and protect the turbocharger and intercooler system when the throttle abruptly closes. The Engine Control Module (ECM), often referred to as the Powertrain Control Module (PCM), continuously monitors the voltage, current, or resistance values within this circuit. When the ECM detects an electrical signal or feedback value that falls outside its pre-programmed operational parameters—such as an open circuit, a short to ground, a short to voltage, or an implausible signal from a position sensor integrated into the relief valve assembly—it sets code P1694. This indicates that the ECM has lost proper control or feedback from the component responsible for relieving excess boost pressure, which is typically a bypass valve (BPV) or blow-off valve (BOV) solenoid or actuator circuit.

Common Symptoms

• Illuminated Malfunction Indicator Lamp (MIL): The Check Engine Light will be on.
• Reduced Engine Performance: Noticeable lack of power, slower acceleration, or the engine entering a "limp home" mode to prevent further damage.
• Audible Compressor Surge: A distinct "whooshing" or "fluttering" sound from the turbocharger area during throttle lift-off or gear changes, indicating the charge air relief valve is not functioning correctly to vent excess pressure.
• Inconsistent Boost Pressure: Erratic or fluctuating boost gauge readings, if equipped.
• Hesitation or Stumbling: The engine may hesitate or stumble during transitions, especially when getting on or off the throttle.
• Decreased Fuel Economy: Inefficient boost management can lead to the ECM compensating, potentially increasing fuel consumption.

What Causes the Code P1694?

• Faulty Charge Air Relief Valve Solenoid/Actuator: Internal electrical failure of the solenoid coil or actuator motor, leading to incorrect resistance or an open/short circuit.
• Wiring Harness Issues: Damaged, chafed, corroded, or disconnected wiring in the charge air relief valve circuit, leading to an open circuit, short to ground, or short to voltage. This includes poor terminal tension or corrosion at the connector.
• Defective Pressure or Position Sensor: If the relief valve system incorporates a feedback sensor (e.g., a position sensor for the valve itself or an associated pressure sensor), a malfunction in this sensor can send implausible data to the ECM, triggering the code.
• Vacuum System Leak or Blockage: For vacuum-actuated relief valves, a leak in the vacuum lines or a blockage in the vacuum supply system can prevent the valve from operating correctly, and if monitored by a sensor, trigger P1694.
• Mechanical Failure of the Relief Valve: A physically stuck-open or stuck-closed valve, while primarily mechanical, can cause an electrical feedback sensor to report out-of-range values, thus indirectly causing a circuit fault code.
• Faulty Engine Control Module (ECM/PCM): Although less common, an internal fault within the ECM’s driver circuit for the charge air relief valve solenoid can cause this code.

How to Diagnose and Troubleshoot

Diagnosing P1694 requires systematic electrical and mechanical checks. Begin by connecting an OBD-II scan tool to confirm the presence of P1694 and check for any related or pending diagnostic trouble codes. Pay close attention to freeze frame data, which provides a snapshot of engine conditions when the fault was recorded.

1. Visual Inspection:
   • Locate the turbocharger/supercharger charge air relief valve (BPV/BOV) and its electrical connector.
   • Inspect the wiring harness for any signs of damage, chafing, cuts, or corrosion from the solenoid back to the ECM.
   • Check the electrical connector for bent pins, corrosion, or loose connections. Ensure it is fully seated.
   • If the valve is vacuum-actuated, inspect all associated vacuum lines for cracks, kinks, disconnections, or blockages.
2. Electrical Circuit Testing (with a Digital Multimeter – DMM):
   • Solenoid Power Supply: With the ignition ON and engine OFF, disconnect the charge air relief valve solenoid connector. Using a DMM, check for battery voltage (typically 12V) or a specified reference voltage at the power supply terminal of the harness side connector.
   • Solenoid Ground/Control: If a voltage signal is present, the other wire will typically be the ground or controlled ground signal from the ECM. Check for continuity to ground if it’s a constant ground or a fluctuating voltage signal if it’s pulse-width modulated (PWM) by the ECM.
   • Solenoid Resistance: Disconnect the solenoid completely from the harness. Measure the resistance across the solenoid terminals. Compare this reading to manufacturer specifications (typically a few ohms, e.g., 20-40 ohms). An open circuit (OL on DMM) or a very low resistance (near 0 ohms, indicating a short) points to an internal solenoid failure.
   • Wiring Continuity: With the battery disconnected and the ECM connector disconnected, perform continuity checks on the wiring harness between the solenoid connector and the ECM connector pins. Check for continuity for both power and signal wires. Also, check for shorts to ground and shorts to voltage on both wires by checking continuity to chassis ground and to known power sources.
3. Functional Testing (with Bi-directional Scan Tool):
   • If available, use a bi-directional scan tool to command the charge air relief valve solenoid ON and OFF. Listen for an audible click or observe the valve’s physical movement (if visible).
   • Monitor live data parameters, such as boost pressure (MAP/BARO sensors) or actual/desired boost, while commanding the valve to see if pressure changes as expected.
4. Vacuum System Testing (if applicable):
   • If the relief valve is vacuum-actuated, use a hand-held vacuum pump to apply vacuum directly to the valve’s actuator. The valve should move smoothly and hold vacuum without leaking. Inspect for proper diaphragm operation.

Recommended Repairs and Solutions

Once the root cause of P1694 has been accurately identified through thorough diagnosis, the following repairs are commonly recommended:

• Repair or Replace Damaged Wiring/Connectors: If the visual inspection or electrical continuity checks reveal damaged, corroded, or poorly connected wiring, repair the harness using appropriate automotive-grade connectors and wiring repair kits. Ensure secure and weather-sealed connections. This is often the most cost-effective and common solution.
• Replace Faulty Charge Air Relief Valve Solenoid/Actuator: If electrical testing confirms an internal fault within the solenoid (e.g., incorrect resistance, no power, no ground, or no response to control signals), replace the solenoid. In many cases, the solenoid is integrated into the valve assembly, requiring replacement of the entire unit.
• Replace Defective Charge Air Relief Valve Assembly: If the mechanical portion of the valve is sticking, seized, or leaking, and electrical components are verified good, the entire valve assembly will need replacement. This often includes the solenoid.
• Repair Vacuum Leaks: For vacuum-actuated systems, replace any cracked, hardened, or disconnected vacuum lines. Ensure the vacuum source to the solenoid/actuator is strong and consistent.
• ECM/PCM Replacement/Reprogramming: If all other components and wiring have been thoroughly tested and confirmed to be functioning correctly, and diagnostic steps point unequivocally to an internal ECM fault, then ECM replacement or reprogramming may be necessary. This is a complex and often expensive repair that should only be performed as a last resort by a qualified technician.

After any repair, clear the DTCs using a scan tool. It is crucial to perform a comprehensive road test under varying engine loads and speeds to ensure the code does not return and that the turbocharger/supercharger system is functioning correctly. Monitor live data for boost pressure, boost control solenoid duty cycle, and any charge air relief valve position feedback during the test drive to confirm the repair’s effectiveness.