OBD-II Code P0188 — What It Means & How to Fix It

What Does This Error Mean?

P0188 means the secondary fuel temperature sensor (Sensor B) is reading an abnormally high voltage signal. High voltage from this sensor makes the ECM think the fuel is extremely hot — hotter than physically possible. The most common cause is an open circuit in the wiring or a failed sensor. This code is less common than P0183 (Sensor A) but behaves the same way. Most drivers experience no drivability issues, but the code must be fixed to pass emissions testing.

Affected Models

Diesel vehicles with dual fuel temperature sensors
Common in Ford Super Duty Power Stroke 6.0L and 6.4L
Common in GM Duramax LLY and LBZ engines
Common in some European diesel passenger cars
Common in heavy-duty diesel work trucks

Common Causes

Open circuit in the Sensor B signal wire (broken wire or disconnected connector)
Failed fuel temperature sensor B with an internal open circuit
Corroded connector pins creating an intermittent open circuit
Sensor B wiring harness chafed and broken near a sharp edge
ECM software issue misreading the Sensor B circuit on specific applications

How to Fix It

Confirm you have P0188 specifically, not P0183. P0183 refers to Sensor A (circuit high), while P0188 refers to Sensor B (circuit high). They're on different circuits and may be in different physical locations. Check your repair manual to find where Sensor B is on your specific engine.

Not all vehicles have a Sensor B. If your vehicle doesn't have a second fuel temperature sensor, P0188 may indicate an ECM programming issue.
Inspect the Sensor B connector and wiring. An open circuit (broken wire or disconnected plug) is the leading cause of high-voltage sensor codes. A sensor that's fully disconnected will read maximum voltage because the ECM sees only its internal pull-up voltage with no sensor to pull it down.

Check whether the connector simply came loose — this is surprisingly common on work trucks subjected to heavy vibration.
Test the sensor by unplugging it and measuring resistance across the sensor terminals with a multimeter. At ambient temperature, the sensor should read a specific resistance value per your repair manual. An open reading (OL or infinite) means the sensor element is broken internally.

Compare your reading to the specification. A reading within 10% of spec is generally acceptable.
Check the wiring between the sensor connector and ECM for an open circuit. With both the sensor and ECM connectors unplugged, measure resistance along the signal wire. More than 1 ohm of resistance on a short run of wire indicates a break or high-resistance joint in the circuit.

Lay the wire along its routing path while measuring — a broken wire sometimes makes contact only when it's lying in a specific position.
Replace Sensor B if it tests as faulty, or repair any broken wiring found. After the repair, clear the code and verify with live data that the Sensor B reading is within a normal range and responds to temperature changes as the engine warms up.

After a repair, the sensor should read ambient temperature when cold and rise gradually as the engine and fuel system warm up.

When to Call a Professional

If sensor replacement doesn't resolve P0188, take the vehicle to a diesel specialist. Dual-sensor fuel temperature systems are more complex to diagnose without the proper wiring diagrams. A diesel shop with factory-level scan tools can access detailed fuel system data not visible on standard OBD-II scanners. Expect to pay $100-$175 for a thorough diagnosis.

Frequently Asked Questions

Why do some vehicles have two fuel temperature sensors?

Some diesel engines use two fuel temperature sensors to measure temperature at different points in the fuel circuit — for example, one at the fuel tank and one at the injection pump or return line. This allows the ECM to detect heat buildup in different parts of the fuel system and adjust injection parameters more precisely. High-performance and heavy-duty diesel applications are most likely to use dual sensors.

Is P0188 a common code?

It's less common than Sensor A codes (P0180-P0183) because not all vehicles have a second fuel temperature sensor. When it does appear, it's usually on high-mileage work trucks where the wiring harness has been subjected to years of heat and vibration. Loose connectors from service work are also a common trigger.

Can this code be caused by actual fuel overheating?

Theoretically yes, but in practice this is very rare. Fuel overheating in a functional fuel system extreme enough to register as an out-of-range high signal would be accompanied by severe drivability issues. The far more likely explanation for P0188 is an open circuit in the wiring or a failed sensor, not actual fuel that is too hot.