P1680

What Does Code P1680 Mean?

The diagnostic trouble code P1680 signifies a malfunction within the Metering Oil Pump (MOP) system. This code is specifically relevant for vehicles equipped with a dedicated MOP, primarily rotary engines (e.g., Mazda Renesis in the RX-8) or certain diesel engine applications that require precise, supplemental lubrication of combustion chamber components. The Engine Control Module (ECM), sometimes referred to as the Powertrain Control Module (PCM), is responsible for controlling the MOP’s output based on various engine parameters such as RPM, load, and throttle position. The ECM monitors the MOP’s operation, often by receiving feedback from an integrated position sensor or by monitoring the current draw of the MOP motor. When the ECM detects an electrical discrepancy—such as an unexpected signal voltage from the position sensor, an open or short circuit in the MOP control circuit, or a deviation from the expected current draw—it flags the P1680 code. This indicates that the MOP is either not responding correctly to ECM commands or its feedback circuit is reporting an implausible state, thereby compromising the critical lubrication of internal engine components.

Common Symptoms

• Check Engine Light (CEL) illumination: The primary and most immediate indicator of the fault.
• Reduced engine performance: Due to potential lack of proper internal lubrication leading to increased friction or premature wear of seals (in rotary engines), resulting in power loss.
• Increased engine oil consumption: If the MOP is stuck in an overly open position or malfunctioning to deliver too much oil, leading to excessive burning of oil.
• Excessive blue or white smoke from the exhaust: A direct result of increased oil consumption in the combustion process.
• Rough idling or misfires: Can occur if lubrication is severely compromised, affecting seal integrity and compression.

What Causes the Code P1680?

• Faulty Metering Oil Pump (MOP) assembly: This is the most prevalent cause, encompassing internal electrical failures of the pump motor or solenoid, mechanical binding, or a defective integrated position sensor.
• Wiring harness damage: Open circuits, short circuits to voltage or ground, or excessive resistance within the MOP control, power, or feedback signal wiring.
• Corroded or loose electrical connectors: Poor electrical contact at the MOP unit, any inline harness connectors, or the ECM connector pins.
• ECM (Engine Control Module) malfunction: While less common, an internal fault within the ECM preventing it from correctly commanding or monitoring the MOP can trigger this code.

How to Diagnose and Troubleshoot

Diagnosing P1680 requires a methodical approach, utilizing an OBD-II scanner, a digital multimeter (DMM), and an understanding of the vehicle’s specific MOP system. Always consult the vehicle’s factory service manual for exact wiring diagrams, component locations, and specified values.

1. Retrieve and Document Data: Connect an OBD-II scanner and record the P1680 code along with any associated freeze frame data. This provides crucial context regarding engine operating conditions (RPM, load, temperature) at the time the fault occurred. Clear the code after documentation.
2. Visual Inspection: Perform a thorough visual inspection of the metering oil pump unit and its entire wiring harness, from the pump to the ECM. Look for signs of physical damage, loose or corroded electrical connectors, oil saturation (which can degrade wiring), or chafed wiring that may be shorting to ground or other circuits.
3. Verify MOP Power and Ground:
   • Disconnect the MOP electrical connector.
   • Using a DMM, with the ignition key in the ON position (engine OFF), backprobe and check for battery voltage (B+) between the MOP power supply wire terminal and a known good chassis ground.
   • Check for proper ground continuity (typically less than 0.5 ohms) between the MOP ground wire terminal and a known good chassis ground.
   • Refer to the vehicle-specific wiring diagram for correct pin identification. An absence of power or ground indicates a wiring issue or a blown fuse/relay upstream.
4. Test MOP Internal Resistance/Continuity: Consult the factory service manual for the specific resistance specifications of the MOP motor or solenoid windings. With the MOP connector disconnected, measure resistance across the relevant terminals on the MOP unit itself using your DMM. An open circuit (infinite resistance) or out-of-spec resistance indicates an internal MOP electrical failure.
5. Check MOP Position Sensor Signal:
   • If the MOP incorporates a position sensor (common in electronically controlled units), backprobe the sensor’s signal wire with the connector attached and ignition ON.
   • Verify the reference voltage (typically 5V) and the ground supply to the sensor.
   • If an external linkage or manual actuation point is present, carefully manipulate the MOP’s control arm and observe the signal voltage change on the DMM. The voltage should change smoothly and linearly through its operating range. A static voltage, erratic readings, or no voltage indicates a faulty sensor or internal MOP mechanism.
6. Wiring Harness Integrity Check: With both the MOP and ECM connectors disconnected, perform continuity and resistance checks on all MOP-related wires between the MOP connector and the ECM connector. Look for open circuits (infinite resistance), short circuits to ground or power (very low resistance to chassis or battery), or excessively high resistance (>5 ohms), which indicates damage within the harness.
7. ECM Pin Inspection: Thoroughly inspect the ECM connector pins for any signs of corrosion, bending, or damage that could impede proper electrical contact.

Recommended Repairs and Solutions

• Replace the Metering Oil Pump (MOP) Assembly: If diagnostic testing conclusively indicates an internal electrical or mechanical fault of the MOP unit itself (motor, solenoid, or integrated position sensor), replacement of the complete MOP assembly is the most common and effective solution.
• Repair or Replace Wiring Harness: If damaged wiring or corroded/faulty connectors are identified during the visual inspection or continuity tests, repair the damaged section of the harness using appropriate soldering and heat-shrink methods, or replace the entire affected harness segment if damage is extensive. Ensure all connections are clean, secure, and properly seated.
• Clean and Secure Connectors: If corrosion or looseness is found at the MOP or ECM connectors, thoroughly clean the terminals using electrical contact cleaner and ensure a tight and secure fit upon reassembly.
• ECM Replacement (Rare): Only consider ECM replacement as a last resort, and only after all other components and wiring have been meticulously tested and verified to be in perfect working order. ECM failures leading specifically to P1680 are uncommon.
• Mechanic’s Tip for Rotary Engines: Always use the manufacturer-specified two-stroke oil for the MOP system in rotary engines. Using incorrect oil types can lead to MOP malfunction, clogging, or premature wear of critical engine components. After MOP replacement on some vehicles, a specific calibration or “re-learn” procedure may be required using a factory-level scan tool to ensure correct oil delivery. Always ensure the MOP oil reservoir (if separate) is adequately filled and monitored.