P0188

Fuel Temperature Sensor B Circuit High Input

P0188 is a generic OBD-II powertrain diagnostic trouble code: Fuel Temperature Sensor B Circuit High Input. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0188
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P0188 means

Code P0188 is set when the engine control module (ECM) or powertrain control module (PCM) detects an abnormally high voltage signal from the fuel temperature sensor "B" circuit. This sensor is mounted in the fuel delivery system — typically on the fuel rail, fuel filter, or fuel pump assembly — and reports fuel temperature to the PCM so it can fine-tune fuel delivery, injection timing, and emissions control. A "circuit high" fault means the PCM is seeing a voltage at or near the supply rail, indicating an open circuit, a broken signal wire, or a failed sensor with an internal open. Unlike a generic performance fault, the high-input designation narrows the fault to the electrical circuit rather than a mechanical fuel issue. Left unrepaired, the PCM cannot accurately compensate for hot fuel, which degrades atomisation, increases emissions, and may force a conservative limp strategy that reduces engine output.

Common causes

Most-frequently reported root causes when P0188 is logged.

  • 1
    Failed fuel temperature sensor B with an internal open circuit driving signal voltage high
  • 2
    Broken, chafed, or disconnected signal wire between the sensor and PCM
  • 3
    Corroded or pushed-out terminal at the sensor connector causing loss of signal
  • 4
    Short to battery voltage on the sensor signal wire
  • 5
    Open circuit in the sensor ground return path
  • 6
    Fuel pump module failure that incorporates the temperature sensor
  • 7
    Faulty PCM or damaged PCM connector pin (rare, diagnose last)

Symptoms drivers notice

Check Engine Light (MIL) illuminated with P0188 stored
Reduced fuel economy due to incorrect fuel temperature compensation
Hard starting or extended crank time, particularly in warm conditions
Rough idle, hesitation, or stumble during acceleration
Increased exhaust emissions potentially triggering secondary oxygen-sensor codes
Possible activation of limp mode with noticeably reduced engine power

How to diagnose P0188

A typical diagnostic flow when this code is present.

  1. 1
    Connect an OBD-II scan tool, confirm P0188 is current (not pending), and note any accompanying codes such as P0187 (low) or fuel pump codes
  2. 2
    Visually inspect the fuel temperature sensor B, wiring harness, and connector for physical damage, corrosion, melted insulation, or loose pins
  3. 3
    With the ignition on (engine off), measure the signal voltage at the sensor connector; a reading near 5 V with the sensor disconnected confirms an open circuit in the sensor or its wiring
  4. 4
    Using a digital multimeter, measure sensor resistance across its terminals and compare to OEM specification (typically 2–3 kΩ at room temperature); infinite resistance confirms an internal open
  5. 5
    Check continuity and absence of shorts between the signal wire and ground, and between signal wire and battery voltage
  6. 6
    Verify PCM reference voltage (5 V) and a clean ground at the sensor connector before condemning the sensor
  7. 7
    Clear the code, perform a test drive covering hot-idle and acceleration, and re-scan to confirm the repair

Related powertrain codes

Frequently asked questions

Can I drive with a P0188 code?

Short distances are possible, but driving is not recommended. The PCM cannot correctly calculate fuel delivery without accurate temperature data, leading to poor economy, rough running, and the risk of limp mode activation, which severely limits power.

What is the difference between P0187 (low) and P0188 (high)?

P0187 indicates a signal voltage below the expected range, usually pointing to a short to ground or a sensor stuck at its low limit. P0188 indicates voltage above the expected range, typically caused by an open circuit, a broken wire, or a sensor shorted internally to the supply voltage.

How is sensor B different from sensor A in P018x codes?

"A" designates the primary or first sensor in a system, while "B" designates a secondary sensor. In fuel systems with two temperature sensors, sensor B is usually located further downstream — for example, on the secondary fuel filter or return line — so the PCM can monitor temperature at a second point.

Will replacing the fuel temperature sensor always fix P0188?

Not always. Start by thoroughly inspecting the wiring harness and connector. A broken wire or corroded terminal is often the real cause, and replacing the sensor without fixing the wiring will result in the code returning immediately.

Disabling P0188 in software

RaceTune can permanently disable P0188 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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