What Does P1685 Mean?
The Engine Control Module (ECM) has detected an electrical fault in the metering oil pump stepping motor circuit. This code is specific to rotary engines (Mazda RX-7/RX-8) where the oil metering pump injects engine oil into the combustion chambers for apex seal lubrication.
Common Causes
35%
Faulty metering oil pump (MOP) stepping motor
30%
Damaged wiring harness or corroded connectors to MOP motor
20%
ECM internal driver circuit failure
10%
Poor ground connection at MOP motor
5%
Short circuit in stepping motor windings
Diagnostic Steps
1
Step 1: Visually inspect MOP wiring harness and connector for damage, corrosion, or loose connections
2
Step 2: Use a multimeter to check stepping motor resistance across all phase windings (typically 20-50 ohms per phase)
3
Step 3: Check ground continuity from MOP motor to chassis ground (should be less than 1 ohm)
4
Step 4: Monitor live data for MOP commanded position vs actual position while engine running
5
Step 5: Perform actuation test using scan tool to verify stepping motor movement and ECM driver circuit operation
Estimated Repair Cost
$300 - $1,200
Parts + labor, varies by vehicle and location
The Engine Control Module (ECM) has detected an electrical fault in the metering oil pump stepping motor circuit. This code is specific to rotary engines (Mazda RX-7/RX-8) where the oil metering pump injects engine oil into the combustion chambers for apex seal lubrication.
The most common cause of P1685 (Metering Oil Pump Stepping Motor Circuit Malfunction) is: Faulty metering oil pump (MOP) stepping motor
Typical repair costs for P1685 range from $300 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Continued operation without proper apex seal lubrication will cause catastrophic engine damage. Do not operate vehicle for extended periods.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1685 to identify the root cause.
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Quick Info
Category
Powertrain
System
Rotary Engine Lubrication System
Difficulty
Type
Manufacturer
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