P1683

What Does Code P1683 Mean?

DTC P1683 signifies a malfunction within the Metering Oil Pump (MOP) Temperature Sensor Circuit. This code is predominantly found in vehicles equipped with rotary engines, such as the Mazda RX-8, where a precise oil injection system is critical for internal lubrication and apex seal cooling. The Engine Control Module (ECM), also referred to as the Powertrain Control Module (PCM), monitors the electrical signal from the MOP temperature sensor. This sensor is typically a thermistor, which changes its electrical resistance in inverse proportion to temperature (resistance decreases as temperature increases). The ECM uses this temperature input to refine the MOP’s operation, ensuring optimal oil viscosity and flow for injection, especially during cold starts or varying engine loads. When the ECM detects an electrical signal from this circuit that is outside of its programmed operational parameters – indicating an open circuit, a short circuit to voltage or ground, or a signal that is implausible for prevailing engine conditions – it will log P1683 and illuminate the Malfunction Indicator Lamp (MIL).

Common Symptoms

• Illumination of the Check Engine Light (CEL): This is the primary and most common indicator.
• Reduced Engine Performance: The ECM may enter a “limp home” mode, limiting engine RPMs or power output to protect the engine due to compromised MOP system monitoring.
• Rough Idle or Stalling: While less direct, an improperly functioning MOP due to lack of temperature data could lead to sub-optimal lubrication, potentially affecting combustion.
• Increased Exhaust Smoke: If the MOP system is forced into a default oil injection strategy due to the sensor malfunction, it might over-inject oil, leading to visible smoke.
• Difficult Cold Starts: Incorrect oil metering due to lack of temperature compensation can make starting the engine in cold weather more challenging.
• Increased Oil Consumption: If the MOP system defaults to a richer oil injection setting, oil consumption may increase.

What Causes the Code P1683?

• Faulty Metering Oil Pump Temperature Sensor: The sensor itself may have failed internally, providing inaccurate readings, a constant high/low voltage, or no signal at all.
• Wiring Harness Issues: Open circuits, short circuits to power or ground, chafed wiring, or corroded conductors within the MOP temperature sensor harness.
• Poor Electrical Connection: Corroded, loose, or damaged terminals at the MOP temperature sensor connector or at the ECM/PCM connector.
• ECM/PCM Malfunction: While less common, an internal fault within the Engine Control Module could prevent it from correctly processing the MOP temperature sensor input.

How to Diagnose and Troubleshoot

Diagnosis of P1683 requires a methodical approach, utilizing an OBD-II scanner and a digital multimeter (DMM).

1. Retrieve and Document DTCs and Freeze Frame Data: Connect an OBD-II scanner and record all stored trouble codes and accompanying freeze frame data. This data provides insights into engine conditions (RPM, engine load, coolant temp) when the fault occurred, which can be valuable. Clear the DTCs after documentation.
2. Visual Inspection:
   • Locate the Metering Oil Pump and its temperature sensor. (In Mazda RX-8, the MOP is typically mounted on the engine block, often near the oil pan or front cover).
   • Carefully inspect the wiring harness leading to the MOP temperature sensor for any signs of damage, fraying, pinching, chafing, or exposed wires. Pay close attention to areas where the harness passes near hot engine components or sharp edges.
   • Inspect the sensor connector for corrosion, bent pins, loose terminals, or signs of water intrusion. Ensure the connector is securely seated.
3. OBD-II Scanner Live Data Analysis:
   • With the ignition ON and engine OFF (KOEO), access the live data stream for the MOP Temperature Sensor.
   • Observe the reported temperature value. A faulty sensor or open circuit might report an extremely low value (e.g., -40°C/-40°F), while a short circuit might report an extremely high value (e.g., 150°C/300°F), regardless of ambient temperature.
   • If the value appears rational, try wiggling the sensor connector and wiring harness while observing the live data. Any fluctuations indicate a loose connection or intermittent wiring issue.
4. Digital Multimeter (DMM) Testing:
   • Sensor Resistance Test: Disconnect the MOP temperature sensor electrical connector. Using the DMM set to ohms, measure the resistance across the two terminals of the sensor itself. Compare this reading to manufacturer specifications (typically found in a factory service manual) for the current ambient temperature. A thermistor-type sensor’s resistance should change predictably with temperature; if the resistance is infinite (open circuit) or zero (short circuit), the sensor is faulty.
   • Reference Voltage Check: With the ignition ON (engine OFF) and the sensor connector disconnected, use the DMM set to volts DC. Place the positive lead into the reference voltage pin of the harness connector and the negative lead to a known good chassis ground. You should typically read approximately 5 volts.
   • Ground Circuit Check: Place the DMM positive lead into the signal return/ground pin of the harness connector and the negative lead to a known good chassis ground. You should read close to 0 volts. Alternatively, use the DMM in continuity mode between the ground pin and chassis ground; it should show very low resistance.
   • Signal Circuit Integrity: If voltage and ground are present at the connector, check the signal wire for continuity to the ECM/PCM. Disconnect both the sensor and ECM/PCM connectors. Use the DMM in continuity mode between the signal wire pin at the sensor harness side and its corresponding pin at the ECM/PCM harness side. There should be very low resistance. Also, check for shorts to ground or voltage on the signal wire by probing it against chassis ground and battery positive.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically performed:

• Repair or Replace Wiring Harness: If the visual inspection or DMM tests reveal damaged, corroded, or shorted sections of the MOP temperature sensor wiring harness, the affected sections should be repaired or the entire harness replaced. Always use high-quality, weather-resistant connectors and proper splicing techniques (e.g., solder and heat shrink) if repairing sections.
• Clean or Replace Connectors: If corrosion or damage is found at the sensor or ECM/PCM connectors, carefully clean the terminals using electrical contact cleaner and a small brush. If pins are bent, broken, or severely corroded, the connector housing and pins should be replaced.
• Replace Metering Oil Pump Temperature Sensor: If the DMM resistance test confirms the sensor itself is faulty (out of manufacturer specifications, infinite resistance, or zero resistance), replace it with a new OEM or high-quality aftermarket sensor. Ensure proper installation and connection.
• ECM/PCM Replacement (Rare): Only consider replacing the ECM/PCM as a last resort, and only after all other potential causes have been thoroughly investigated and ruled out. This is an expensive repair and often requires reprogramming the new module to the vehicle.
• Post-Repair Verification: After completing any repairs, clear all stored DTCs using an OBD-II scanner. Perform a comprehensive test drive under varying conditions, mirroring the freeze frame data if possible, to confirm the repair and ensure the P1683 code does not reappear. Monitor MOP temperature sensor live data during operation to confirm rational readings.