P1688 — Metering Oil Pump Temperature Sensor Circuit Malfunction

Will P1688 clear itself?

Sometimes P1688 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How much does it cost to fix P1688?

Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000; Replace the faulty sensor or actuator — $150–$500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What is the most common cause of P1688?

The most common causes are: open or shorted wiring in the circuit, poor ground connection, control module driver fault.

What are the symptoms of P1688?

Drivers most often notice: increased fuel consumption in some cases, possible limp mode depending on the affected component, Check Engine Light on, the affected system operates intermittently or not at all.

What does OBD2 code P1688 mean?

P1688 — Metering Oil Pump Temperature Sensor Circuit Malfunction. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: open or shorted wiring in the circuit, poor ground connection, control module driver fault.

When your scanner throws code P1688, your engine control unit is reporting that something in the metering oil pump temperature sensing circuit isn't behaving the way it should. The full technical name for this fault is "Metering Oil Pump Temperature Sensor Circuit Malfunction," and it falls under the powertrain category, meaning the issue touches engine or transmission operation.

P1688 is interesting because it's what technicians call a "general malfunction" code. Unlike simpler circuit codes that point directly at electrical problems, this one means the ECU's self-test found the metering oil pump temperature sensor or its associated control logic operating outside normal parameters. The fault could be in the sensor itself, in the wiring connecting it to the computer, or even in the control module that processes the signal. That ambiguity is exactly why P1688 requires systematic diagnosis—you can't just assume the worst part is bad without checking the easy stuff first.

The ECU doesn't set P1688 on a single bad reading. It watches this system continuously as you drive, and only stores the code after the signal stays out of range for a set number of drive cycles. The moment it triggers, the engine light comes on and freeze frame data gets saved—the engine's "black box" recording showing RPM, load, temperature, and speed at the exact instant the fault occurred. That snapshot is your roadmap for diagnosis.

Common Symptoms of P1688

The Check Engine Light is the most obvious clue that P1688 is active. Beyond the dashboard warning, you might notice reduced fuel efficiency, or in some cases the system involved may enter a protective limp mode that limits performance. The metering oil pump temperature sensor controls a specific function—its failure means that system either stops working reliably or cuts out entirely, leaving you with intermittent operation or a complete loss of that auxiliary feature.

What Causes P1688

The most likely culprit is an internal failure of the metering oil pump temperature sensor itself. Wiring problems come second—damaged insulation, loose connectors, or corrosion at the plug can all confuse the ECU's self-test. A poor ground at the sensor will do the same thing. Open or shorted wires in the circuit trigger the code just as easily as a bad component. Less commonly, the control module's driver circuit for this sensor fails, or a software glitch in the ECU causes a false positive. A blown fuse feeding the circuit is another possibility worth checking early in your diagnosis.

How to Diagnose P1688

A systematic approach keeps you from wasting money on parts you don't need. Start by connecting your OBD2 scanner and confirming P1688 is stored, then save the freeze frame data before you do anything else. That snapshot tells you exactly what conditions existed when the fault triggered—RPM, load, temperature, vehicle speed—and those conditions are what you should reproduce during your test drive later.

Next, check for any other diagnostic trouble codes present in the system. Related codes often reveal the root cause rather than this secondary fault. While you're at it, search for manufacturer technical service bulletins for your specific make and model—some P0xxx issues have known factory fixes or software updates available.

Then comes the hands-on inspection. Look closely at the wiring harness and connectors associated with the metering oil pump temperature sensor. Check for damaged insulation, broken strands inside wires, corrosion buildup on the terminals, and any signs that connectors aren't fully seated. If your scanner supports actuator tests, command the sensor to respond—something that fails to react to a direct command is confirmed faulty.

Finish by measuring reference voltage, ground resistance, and signal continuity at the sensor connector. Use a wiggle test on the harness while watching live data; any dropouts or interruptions point to broken wires inside the insulation that aren't visible from the outside. Finally, clear the code, drive through the freeze frame conditions, and verify P1688 doesn't return.

Repair Options and Costs

What you actually fix depends entirely on what you find during diagnosis. Here are the typical repair scenarios for P1688, including parts and labor at independent shop rates:

• Wiring repair or connector replacement: $80–$250
• Metering oil pump temperature sensor replacement: $150–$500
• Control module diagnosis and repair: $300–$1,000

The total bill typically lands somewhere between $80 and $1,000 depending on which component failed. The important point: always confirm the actual problem before buying expensive parts. The most expensive scenario is rarely the first one to check.

Can You Drive with P1688?

In most cases, yes—the car remains drivable, though you may experience slightly reduced performance or lose access to certain auxiliary functions. If the underlying fault causes stalling, a no-start condition, or triggers warnings related to braking or steering, treat it as urgent and get it looked at immediately. Otherwise, you can schedule the repair at your convenience, but don't ignore the Check Engine light indefinitely.

Related OBD2 codes

• P1600: Throttle Control Unit Malfunction
• P1601: Throttle Control Unit Throttle Position Malfunction
• P1602: Throttle Control Unit Modulated Command Malfunction
• [P1603: