P0187 — Fuel Temperature Sensor B Circuit Low Input

P0187 — Fuel Temperature Sensor B Circuit Low Input. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit, control module driver fault.

powertrain (engine/transmission)

Is it safe to drive?

Limit driving until the fault is repaired P0187 can cause incorrect engine fueling and poor running, especially when the signal is intermittent. Avoid extended driving or heavy loads, but stop driving if the engine stalls, misfires severely, smokes heavily, or loses power.

Typical symptoms

The check engine light may illuminate with P0187 stored in the ECU
The scan tool may show an implausibly low or fixed fuel temperature value
The engine may idle roughly, hesitate, or misfire while using an invalid temperature signal
Hot restarting, stalling, or uneven operation may occur with a faulty sensor signal
Exhaust smoke or unusual engine running behavior may appear if the ECU compensates for the false reading

Common causes

A short to ground in the fuel temperature sensor B signal wire
An open circuit or intermittent connection in the sensor B wiring harness
Corrosion, damage, or loose terminals at the sensor or ECU connector
A failed fuel temperature sensor B with incorrect internal resistance
A faulty sensor B ground or 5-volt reference circuit
An incorrectly wired or incompatible replacement sensor

How to diagnose with an OBD scanner

Inspect sensor B and its wiring Locate fuel temperature sensor B on the fuel rail, injection system, or fuel tank area as specified by the vehicle documentation. Inspect the connector and harness for corrosion, bent pins, pinched wiring, heat damage, and fuel or oil contamination.
Confirm P0187 with an OBD scanner Connect an ELM327 adapter to the OBD-II port and use AIScanAuto to check stored and pending codes. Confirm P0187 and, if supported, compare the live fuel temperature reading with the vehicle's expected value.
Measure the sensor circuit With the ignition appropriately enabled, back-probe the sensor B signal at the connector and ECU. Compare the voltage and sensor resistance with service specifications. A signal pulled toward ground indicates a short, while an open circuit can also trigger a low-input code.
Isolate the sensor from the harness Disconnect sensor B and perform the specified resistance checks. If the sensor is out of specification, replace it with the correct part. If the sensor passes, continue testing the connector, wiring, ground, reference circuit, and related ECU terminal.
Repair and verify the correction Repair damaged wiring or terminals, or replace the defective sensor. Clear P0187 with the scanner, then verify normal fuel temperature data and road-test the vehicle for hesitation, stalling, and a returning code.

Approximate repair cost

A typical independent-shop estimate for P0187 repair is USD 150–450, depending on whether the fault requires sensor replacement, connector service, or wiring repair. Labor time and accessibility of the sensor can also affect the total. These figures are estimates and vary by region.

Common questions

What does P0187 specifically mean?

P0187 means the ECU detected a low electrical input from fuel temperature sensor B. It describes the sensor circuit and does not, by itself, prove that the fuel is actually at an unsafe temperature.

Can I drive the vehicle with P0187?

Limited driving may be possible if the engine runs normally, but an incorrect fuel temperature signal can cause hesitation, stalling, or improper fueling. Repair P0187 promptly and avoid heavy loads.

Does P0187 require replacing the fuel temperature sensor?

Not always. The sensor may be serviceable, but a shorted wire, corroded connector, or failed sensor can all create the low-input condition. Circuit testing should determine which repair is needed.

How should P0187 be verified after repair?

Clear the code with an OBD scanner, confirm that the fuel temperature reading is plausible, and road-test the vehicle. P0187 should not return if the sensor, wiring, connectors, and circuit operation are correct.

When your scan tool displays P0187, the engine control unit is telling you that the fuel temperature sensor B circuit is showing a voltage reading that falls below the minimum threshold it expects to see during normal operation. P0187 is classified as a powertrain fault, which means it involves the engine or transmission control systems. The term "circuit low" specifically indicates that the electrical signal on this particular circuit is sitting near ground potential instead of holding the proper voltage level that the computer needs to calculate fuel temperature accurately.

Modern engines rely on fuel temperature data to make precise adjustments to fuel delivery, especially during cold starts and varying operating conditions. The fuel temperature sensor works alongside other sensors to give the ECU a complete picture of what's happening inside the fuel system. When the signal wire for this sensor shorts to ground or when the sensor itself fails in a way that pulls the voltage down, the control module detects the anomaly, sets P0187, and captures a freeze frame snapshot of engine RPM, load, coolant temperature, and vehicle speed at the exact moment the fault occurred. This freeze frame data is extremely useful because it tells you exactly what conditions were present when the problem was detected, which helps narrow down whether the issue is environmental, intermittent, or related to a specific driving pattern.

P0187 will often set alongside other fuel-system-related trouble codes, so addressing related codes first frequently resolves the underlying issue without needing further diagnosis. Many manufacturers publish technical service bulletins that cover common sensor faults like this one, and checking those bulletins for your specific vehicle can save hours of trial-and-error troubleshooting.

Common Symptoms

The Check Engine Light illuminates and remains on until the fault is cleared
Some vehicles experience increased fuel consumption due to incorrect fuel mixture adjustments
The fuel system may enter a reduced-power limp mode depending on how the vehicle manufacturer programmed the failure response
The affected component or an associated system may operate intermittently or stop functioning entirely
In rare cases, hard starting or rough idle may occur if the ECU defaults to a fixed fuel strategy

Possible Causes

The fuel temperature sensor B itself has failed and is dragging the signal voltage low
The signal wire has shorted to ground somewhere in the harness due to chafed or damaged insulation
A corroded, loose, or damaged connector is interrupting the circuit properly
The fuse that supplies voltage to this circuit has blown
A poor ground connection is preventing the circuit from biasing correctly
Supply voltage to the fuel temperature sensor is missing entirely
The control module driver for this circuit has failed internally

How to Diagnose

Connect an OBD2 scanner and confirm P0187 is stored in the ECU memory, then record the associated freeze frame data before clearing anything—this snapshot reveals engine conditions at the moment of failure and guides your inspection.
Pull all stored codes from the vehicle. P0187 often appears alongside other fuel or sensor-related codes that point directly to the root cause. Also search for technical service bulletins specific to your make, model, and model year by entering your VIN on the manufacturer website or checking NHTSA.gov.
Perform a thorough visual inspection of the wiring harness and connectors tied to the fuel temperature sensor B. Look for frayed wires, insulation damage, corrosion buildup, bent pins, or any signs of moisture intrusion at the connectors.
With the connector unplugged, check for proper supply voltage at the sensor harness. Then measure resistance from the signal wire to ground—if you read near-zero ohms, there is a confirmed short to ground somewhere in the harness that must be located and repaired.
If the harness checks out, verify reference voltage, ground, and signal continuity directly at the sensor connector. Compare your readings against manufacturer specifications for your specific vehicle.
Perform a wiggle test on the harness while monitoring live data from the sensor. Any signal dropouts or instability indicate a broken wire that is making intermittent contact.
After repairs, clear P0187 and complete a full drive cycle that replicates the conditions captured in the freeze frame. The code should not return if the repair was successful.

Repair Options and Costs

If the wiring or connector is damaged, repairing or replacing the affected section typically costs between $80 and $250 for parts and labor. When the fuel temperature sensor B itself has failed, replacement runs approximately $150 to $500 depending on your vehicle and whether you use OEM or aftermarket parts. In the worst-case scenario where the control module driver has failed, repair or replacement of the ECU can cost anywhere from $300 to $1,000.

Overall, fixing P0187 usually falls somewhere between $80 and $1,000 depending on which component actually caused the fault. An accurate diagnosis before purchasing parts will almost always save you money, because the most expensive repair scenarios are rarely the first ones you should investigate.

Driving Safety Verdict

P0187 is generally classified as a short-term drivability fault. Most vehicles will remain operational with this code present, though you may notice slightly reduced performance or a disabled auxiliary system depending on how your specific vehicle responds to sensor faults. If the car exhibits stalling, failure to start, or warnings affecting the brakes or steering, treat the situation as urgent and have it diagnosed immediately. Otherwise, schedule repair at your earliest convenience to prevent potential fuel delivery issues from worsening.