P1690

What Does Code P1690 Mean?

DTC P1690 signifies that the Powertrain Control Module (PCM), also referred to as the Engine Control Module (ECM), has detected an electrical malfunction within the wastegate solenoid control circuit. In turbocharged or supercharged engines, the wastegate solenoid is a critical electro-pneumatic or electro-mechanical component responsible for precisely regulating exhaust gas flow to the turbocharger turbine, thereby controlling boost pressure. The PCM actively monitors the electrical characteristics (voltage, resistance, current draw) of this circuit. When the PCM commands the wastegate solenoid to operate (e.g., to open or close the wastegate actuator) and the actual electrical feedback from the circuit deviates from the expected parameters—such as an open circuit, short to ground, short to voltage, or an incorrect resistance value—the P1690 code is set. This indicates a failure in the circuit integrity, preventing the PCM from effectively managing boost pressure, which can lead to either an overboost or underboost condition. The PCM will often initiate a “limp-home” mode to protect the engine, limiting power output and boost levels.

Common Symptoms

• Check Engine Light (CEL) Illumination: The primary and most common indicator that a fault has been detected.
• Reduced Engine Power or "Limp Mode": The PCM limits engine performance, often by reducing boost or fuel delivery, to prevent potential damage.
• Poor Acceleration or Turbo Lag: If the wastegate is stuck open or not closing efficiently, the turbocharger may not build boost effectively.
• Excessive Boost/Surging (less common but possible): If the solenoid fails in a manner that keeps the wastegate closed or minimally open, leading to uncontrolled boost pressure.
• Unusual Engine Noises: Hissing, whistling, or mechanical rattling from the turbocharger area if related to a physical issue with the wastegate itself due to solenoid malfunction.
• Decreased Fuel Economy: The engine may operate inefficiently due to improper boost control, leading to increased fuel consumption.

What Causes the Code P1690?

• Faulty Wastegate Solenoid Valve: Internal electrical failure of the solenoid itself, such as an open circuit in its coil windings, an internal short circuit, or degradation of its internal components.
• Damaged Wiring Harness: Frayed, cut, chafed, or corroded wiring in the wastegate solenoid control circuit. This is often caused by heat exposure, vibration, or rodent damage.
• Corroded or Loose Electrical Connector: Poor connection at the wastegate solenoid due to corrosion on the pins, a bent pin, or a loose fitting connector housing.
• Short to Ground: The solenoid’s control wire inadvertently making contact with a chassis ground point, causing an unintended circuit completion or voltage drop.
• Short to Voltage: The solenoid’s control wire coming into contact with a constant power source, leading to incorrect voltage readings by the PCM.
• Open Circuit: A complete break in the power or ground wire leading to the solenoid, preventing any current flow.
• Faulty Powertrain Control Module (PCM/ECM): Although less common, an internal failure within the PCM’s driver circuit for the wastegate solenoid can trigger this code.

How to Diagnose and Troubleshoot

Diagnosis of P1690 requires a systematic approach, combining visual inspection with electrical testing using a Digital Multimeter (DMM) and an OBD-II scanner with live data capabilities.

1. Visual Inspection:
   • Begin by thoroughly inspecting the wastegate solenoid and its immediate surroundings. Look for any obvious signs of physical damage to the solenoid body, electrical connector, and vacuum lines (if applicable).
   • Trace the wiring harness leading to the solenoid as far as possible, checking for chafing, cuts, signs of heat damage, or rodent activity. Pay close attention to areas where the harness passes near hot engine components or sharp edges.
   • Inspect the electrical connector for corrosion on the pins, bent terminals, or a loose fit. Disconnect and re-connect it to ensure a solid connection.
2. OBD-II Scanner Live Data Analysis:
   • Connect an advanced diagnostic scanner and monitor relevant live data parameters. Look for boost pressure readings, desired vs. actual boost, and the wastegate solenoid duty cycle (if available).
   • Check for other related DTCs that might provide additional context to the problem.
   • If your scanner supports bidirectional control, attempt to actuate the wastegate solenoid ON/OFF. While observing live data (e.g., boost pressure changes) or listening for the solenoid’s click, confirm if the PCM can command the solenoid and if there is any response.
3. Digital Multimeter (DMM) Testing:
   • Solenoid Resistance Test: Disconnect the wastegate solenoid’s electrical connector. Using your DMM set to ohms, measure the resistance across the two terminals of the solenoid itself. Compare this reading to the manufacturer’s specifications (typically a low resistance value, e.g., 5-20 ohms). An "OL" (open line) reading indicates an open circuit within the solenoid, while a very low or zero resistance reading could indicate an internal short.
   • Power Supply Test: With the ignition ON and the solenoid still disconnected, measure the voltage between the power supply wire (often 12V, identified by wiring diagrams) at the solenoid connector and a known good chassis ground. Ensure there is proper voltage present.
   • Control Circuit Continuity/Short Test: With the ignition OFF and the PCM connector potentially disconnected (consult service manual for specific procedures to avoid PCM damage), test for continuity in the control wire between the solenoid connector and the PCM connector. Also, check for shorts to ground or shorts to voltage on both the power and control wires from the solenoid to the PCM.
   • Ground Circuit Test: If the PCM controls the solenoid by switching ground, with the ignition ON, check for continuity to ground on the ground side of the circuit at the solenoid connector when the PCM is commanding the solenoid active (this might require the engine to be running or specific conditions met).

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are commonly indicated for a P1690 fault:

1. Repair or Replace Damaged Wiring/Connectors: If your DMM tests or visual inspection revealed issues with the wiring harness or electrical connectors, perform precise repairs. Use appropriate heat-shrink tubing and high-quality electrical connectors. Ensure all repairs are weatherproofed, especially in engine bay environments.
2. Replace the Wastegate Solenoid Valve: If the solenoid itself failed the resistance test or did not actuate during bidirectional control, replacement is necessary. Always use an OEM equivalent or a high-quality aftermarket solenoid that matches the original specifications. Ensure proper routing of any vacuum lines if it’s a vacuum-controlled unit.
3. Address Vacuum System Leaks (if applicable): While P1690 is an electrical circuit fault, if the wastegate solenoid relies on vacuum, ensuring the integrity of the associated vacuum lines is crucial for its proper function. Repair or replace any brittle, cracked, or disconnected vacuum hoses.
4. PCM Replacement/Reprogramming (Last Resort): If all wiring, connectors, and the wastegate solenoid itself test perfectly, and the P1690 code persists, the PCM’s internal driver circuit for the solenoid may be at fault. This is a rare and costly repair; thus, extremely thorough diagnosis of all other possibilities is imperative before considering PCM replacement. A new PCM will require programming to the vehicle.

After any repair, clear the DTCs using your OBD-II scanner. Perform an extended test drive under various load and speed conditions to verify that the fault does not return and that the engine’s boost control system is operating correctly. Monitoring live data during the test drive can confirm proper wastegate solenoid function and boost pressure regulation.