P1687

What Does Code P1687 Mean?

DTC P1687 signifies a detected malfunction within the Metering Oil Pump (MOP) Stepping Motor Circuit. This code is typically relevant to vehicles equipped with an engine design that utilizes a precision-controlled oil injection system, such as rotary engines (e.g., Mazda Renesis) or certain high-performance two-stroke engines. The Metering Oil Pump is responsible for injecting a precise amount of lubricating oil directly into the engine’s combustion chambers or intake manifold, crucial for lubricating critical components like apex seals, rotor bearings, or cylinder walls, depending on the engine type. The ECM/PCM (Engine Control Module/Powertrain Control Module) controls the oil flow rate by sending specific pulse width modulation (PWM) signals to a stepper motor integrated within the MOP. The stepper motor’s precise rotational position dictates the volume of oil dispensed. When the ECM/PCM detects an unexpected electrical condition within this circuit—such as an open circuit, a short circuit to voltage or ground, or an out-of-range resistance or current draw—it determines that the stepping motor is not responding as commanded or its circuit integrity is compromised, subsequently setting code P1687 and illuminating the Malfunction Indicator Lamp (MIL).

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Reduced Engine Performance: The ECM may enter a “limp mode” to protect the engine, limiting RPM or power output.
• Excessive Exhaust Smoke: If the MOP stepper motor fails in a position that causes excessive oil injection.
• Engine Misfires or Rough Idle: Incorrect oil-air mixture due to erratic oil injection can lead to combustion issues.
• Engine Knocking or Abnormal Noises: A critical lack of lubrication due to MOP failure can lead to accelerated wear and internal engine damage.
• Engine Damage or Failure: Prolonged operation with insufficient lubrication, a severe consequence of MOP malfunction, can lead to catastrophic engine failure over time.

What Causes the Code P1687?

• Faulty Metering Oil Pump (MOP) Stepping Motor: Internal electrical failure of the motor windings, mechanical binding of the motor, or worn internal gears.
• Wiring Harness Damage: Open circuits, short circuits to ground or power, or excessively high resistance within the MOP stepping motor’s electrical wiring. This can be caused by chafing, corrosion, or heat damage.
• Corroded or Loose Electrical Connectors: Poor connection at either the MOP assembly or the ECM/PCM due to oxidation, bent pins, or inadequate terminal tension.
• Faulty Engine Control Module (ECM/PCM): Although less common, an internal ECM fault preventing proper control signal output or feedback interpretation for the MOP stepping motor circuit.
• Mechanical Seizure of the MOP: While primarily an electrical code, a mechanically jammed MOP preventing the stepper motor from rotating can lead to the ECM detecting an electrical overload or current draw outside of specifications.

How to Diagnose and Troubleshoot

Diagnosis of P1687 requires methodical electrical testing and a thorough understanding of the metering oil pump system. Always begin by referring to the vehicle-specific factory service manual for precise wiring diagrams, connector pin-outs, and resistance specifications.

1. Initial Scan and Freeze Frame Data Analysis: Connect an OBD-II scan tool to confirm the presence of P1687. Review any associated freeze frame data, which captures engine operating conditions (RPM, load, temperature) when the fault was set. This can provide clues regarding when the malfunction occurred. Clear the DTC and attempt to reproduce the fault under similar conditions.
2. Visual Inspection:
   • Carefully inspect the MOP assembly and its electrical connector and wiring harness. Look for obvious signs of damage such as chafing, cuts, bare wires, or evidence of overheating.
   • Examine the MOP electrical connector for bent, pushed-out, or corroded pins. Check for proper terminal tension. Trace the harness back towards the ECM, inspecting for any points of contact with moving parts or sharp edges that could cause wear.
   • If accessible, inspect the ECM/PCM connector for similar issues, paying attention to the pins associated with the MOP circuit.
3. Electrical Circuit Integrity Test (Using a Digital Multimeter – DMM):
   • Disconnect the MOP connector. Refer to the service manual for the correct MOP connector pin-out.
   • MOP Stepping Motor Resistance Test: Measure the resistance across the MOP stepping motor terminals (according to the service manual, typically across pairs of windings). Compare the measured resistance to manufacturer specifications. An open circuit (DMM displays OL or infinite resistance) or a reading significantly outside the specified range indicates an internal fault within the MOP stepper motor itself.
   • Wiring Harness Continuity Test: With the MOP connector disconnected and the ECM connector (if accessible) also disconnected, test for continuity between the MOP connector pins and their corresponding ECM pins. Any lack of continuity indicates an open circuit in the wiring harness.
   • Wiring Harness Short to Ground/Power Test: With both connectors disconnected, test for continuity between each MOP circuit wire and a known good chassis ground, and then between each MOP circuit wire and a fused B+ source. Any continuity indicates a short circuit that needs to be located and repaired.
   • Voltage Supply and Ground Test: With the ignition ON (and MOP disconnected), check for proper voltage supply at the MOP connector (if dedicated power is provided to the control circuit). Verify the integrity of the ground circuit by checking its resistance to chassis ground (should be very low, < 5 ohms).
4. Actuator Test (Bi-directional Scan Tool): If available, use a bi-directional scan tool to command the MOP stepping motor to cycle through its positions. Listen for the motor operating and observe any visible movement of the MOP arm or components. Monitor scan tool feedback for MOP position or duty cycle. Failure to operate or incorrect feedback during this test, combined with good wiring, points to a faulty MOP assembly.
5. ECM/PCM Pin-out Testing: If all previous tests confirm the wiring harness and MOP stepping motor are in good order, and the bi-directional test fails, carefully test the output signals from the ECM/PCM for the MOP circuit. This often requires an oscilloscope to observe the PWM signals. Compare these signals to factory specifications. A lack of proper output signals could indicate an internal ECM/PCM fault.

Recommended Repairs and Solutions

Once the root cause of P1687 has been accurately identified, the following repairs are typically recommended:

• Repair or Replace Wiring and Connectors: If the visual inspection or DMM tests reveal damaged wiring, corroded terminals, or loose connections, the affected section of the wiring harness should be repaired or replaced. Use high-quality, heat-resistant wiring, proper crimping techniques, and heat-shrink tubing for durable repairs. Replace severely corroded or damaged connectors.
• Replace Metering Oil Pump (MOP) Assembly: In the majority of cases where P1687 is set, the internal stepping motor within the MOP assembly has failed. If the resistance tests indicate an out-of-specification reading, or if the MOP fails to operate during the bi-directional control test while wiring is confirmed good, the entire MOP assembly will need to be replaced. Ensure the new MOP is specific to the vehicle make and model.
• ECM/PCM Replacement (Last Resort): If all other components (wiring, connectors, MOP assembly) have been thoroughly tested and confirmed to be functioning correctly, and the ECM/PCM is definitively determined to be at fault (e.g., no output signal to MOP), then ECM/PCM replacement may be necessary. This typically requires specialized programming and calibration.

Mechanic’s Tips:

• Always consult the vehicle’s specific factory service manual for detailed procedures, torque specifications, and electrical values. This is especially critical for MOP systems, as they are unique to certain engine architectures.
• When replacing the MOP, ensure proper bleeding procedures are followed for the oil lines to prevent airlocks and ensure immediate, adequate lubrication upon engine startup. Air in the lines can temporarily lead to insufficient oil delivery.
• Verify the oil reservoir level (if applicable for a separate MOP reservoir) and ensure the correct type of metering oil is being used, as specified by the manufacturer.
• After any repair, clear the DTCs from the ECM/PCM and perform an extended test drive under varying engine conditions (RPM, load, temperature) to confirm that the P1687 code does not return and that the MOP system is operating as intended.