P1668 — Output Circuit Check Signal High

Will P1668 clear itself?

Sometimes P1668 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 P1668?

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

What are the symptoms of P1668?

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

What does OBD2 code P1668 mean?

P1668 — Output Circuit Check Signal High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, open or shorted wiring in the circuit, blown fuse feeding the circuit.

Is it safe to drive with P1668?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

When the engine control unit detects an unusually high voltage on the output circuit check circuit, it stores OBD2 code P1668. This diagnostic trouble code falls within the powertrain category, specifically dealing with the relationship between sensors, actuators, and the modules that command them. The term "signal high" tells you exactly what the computer saw: a voltage reading that climbed close to battery level when it should have been operating within a normal, lower range.

The output circuit check circuit serves as a communication pathway between the ECU and various engine sensors or actuators. When everything functions properly, this circuit carries precise voltage signals that the control module interprets to manage fuel delivery, ignition timing, transmission shifting, or other critical functions. A short to a positive power source, an interrupted ground path, or a defective component pulling the line high will all trigger the same result — the ECU recognizes an implausible reading and sets P1668 to alert the driver. The module typically validates this condition across multiple drive cycles before activating the Check Engine light, and it captures a freeze frame snapshot capturing RPM, engine load, coolant temperature, and vehicle speed at the moment of failure.

Diagnosing P1668 effectively requires understanding that this code describes a symptom rather than a specific failed part. The high signal could originate from wiring, connectors, ground connections, the sensor or actuator itself, or even the control module's internal driver circuit. Working through these possibilities systematically keeps repair costs reasonable.

Common Symptoms of P1668

• The Check Engine Light illuminates on the dashboard
• The system associated with the affected circuit operates intermittently or stops working entirely
• Fuel economy may increase noticeably during the fault condition
• Some vehicles enter reduced-power limp mode depending on which component is affected
• Other diagnostic codes may accompany P1668, pointing to related circuit failures
• In rare cases, minor drivability symptoms such as rough idle or hesitation occur

What Causes P1668

The most frequent culprits behind code P1668 involve wiring and connection problems, though component failures also occur regularly:

• A signal wire accidentally shorted to battery positive somewhere in the harness
• An open or corroded ground return path for the output circuit check
• The sensor or actuator itself drawing the circuit high due to internal failure
• Damage, corrosion, or looseness at the electrical connector feeding the circuit
• A failed output driver inside the engine control module
• Blown fuse interrupting power to the affected circuit
• Wiring broken inside the harness insulation, creating an intermittent open circuit

How to Diagnose P1668

A methodical approach prevents unnecessary part replacements when dealing with P1668:

1. Connect an OBD2 scanner, verify that P1668 is stored in the ECU memory, and record the freeze frame data before clearing anything — this snapshot reveals exactly what conditions triggered the fault.
2. Search for any manufacturer technical service bulletins (TSB) covering P1668 for your specific make and model, as some vehicles have known software updates or factory remedies documented.
3. Perform a thorough visual inspection of the wiring harness and connectors associated with the output circuit check, looking for damaged insulation, corrosion, bent pins, or loose connections.
4. Disconnect the affected component and measure signal voltage at the harness side — if voltage remains high with the component unplugged, the harness itself contains a short to power; if voltage drops to normal, the component is faulty.
5. Test reference voltage, ground integrity, and signal continuity directly at the component connector using a multimeter to isolate the problem.
6. Perform a wiggle test on the harness while monitoring live data — any signal dropouts indicate broken wires inside the insulation that require repair.

Repair Options and Costs

Repair costs for P1668 vary significantly depending on which part actually failed:

• Wiring harness repair or connector replacement: $80–$250
• Replacement of the faulty sensor or actuator: $150–$500
• Engine control module diagnosis or repair: $300–$1,000

Total Repair Cost for P1668

Most P1668 repairs fall between $80 and $500 when the fault originates in wiring or a failed sensor. Control module issues push costs toward $1,000 but represent a minority of cases. An accurate diagnosis before purchasing parts makes the difference between a $100 wiring repair and an unnecessary $800 module replacement.

Can You Drive with P1668?

P1668 carries a short-term driving safety rating, meaning most vehicles remain operational with this code stored. However, performance reductions or disabled auxiliary systems may occur depending on which circuit is affected. If the vehicle exhibits stalling, failure to start, or warnings related to braking or steering, seek immediate repair — these symptoms transform a manageable fault into a safety concern.

Related OBD2 codes

• P1600: Throttle Control Unit Malfunction
• P1601: Throttle Control Unit Throttle Position Malfunction
• P1602: Throttle Control Unit Modulated Command Malfunction
• P1603: Throttle Control Unit Detected Loss of Return Spring
• P1604: TCU Unable To Control Desired Throttle Angle
• P1605: Loss of KAM Power; Open Circuit