What Does P1688 Mean?
The ECM has detected an abnormal signal from the metering oil pump temperature sensor circuit. This sensor monitors oil temperature to adjust injection rates for proper rotary engine lubrication across temperature ranges.
Common Causes
40%
Faulty metering oil pump temperature sensor
30%
Open or short circuit in sensor wiring
15%
Corroded or loose sensor connector
10%
ECM sensor input circuit failure
5%
Sensor mounting damage causing poor thermal contact
Diagnostic Steps
1
Step 1: Check sensor connector for corrosion, damage, or poor terminal fit
2
Step 2: Measure sensor resistance at various temperatures (compare to manufacturer specification chart)
3
Step 3: Check sensor signal voltage at ECM with engine cold then warm (should change smoothly)
4
Step 4: Inspect sensor wiring for chafing, breaks, or shorts to ground/power
5
Step 5: Verify 5V reference voltage supply from ECM to sensor circuit
Estimated Repair Cost
$150 - $400
Parts + labor, varies by vehicle and location
The ECM has detected an abnormal signal from the metering oil pump temperature sensor circuit. This sensor monitors oil temperature to adjust injection rates for proper rotary engine lubrication across temperature ranges.
The most common cause of P1688 (Metering Oil Pump Temperature Sensor Circuit Malfunction) is: Faulty metering oil pump temperature sensor
Typical repair costs for P1688 range from $150 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Incorrect oil metering due to temperature sensor failure can cause engine damage over time. Safe to drive short distances but repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1688 to identify the root cause.
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Quick Info
Category
Powertrain
System
Rotary Engine Lubrication System
Difficulty
Type
Manufacturer
Recommended Tools
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