P0187 — Fuel Temperature Sensor “B” Circuit Low #

The code label can vary depending on the vehicle manufacturer.

• Fuel Temperature Sensor “B” Circuit Low Input (General/SAE)
• Fuel Temp Sensor B Circuit Low Voltage (Ford, GM)
• Diesel Fuel Temp Sensor B Signal Low (Mercedes-Benz, BMW)
• Fuel Temperature Sensor 2 Circuit Low (Nissan, Toyota)

Summary of DTC P0187 #

DTC P0187 indicates that the fuel temperature sensor “B” is reporting a persistently low electrical signal to the powertrain control module (PCM). The fuel temperature sensor measures the temperature of the fuel, providing crucial data for optimizing injection timing, emissions, and overall engine performance. When the circuit voltage falls below a specific threshold set by the OEM, the PCM flags this code. This can be caused by electrical issues, sensor failure, or wiring problems. Although not as common as other fuel system codes, P0187 should not be ignored to prevent driveability issues or damage to the fuel system.

Common Symptoms for DTC P0187 #

A vehicle with P0187 may display a range of symptoms, some more noticeable than others. Often, the vehicle’s check engine light will be the first sign, but you may also notice performance issues that hint at a fuel system irregularity. The impact can vary depending on whether the vehicle uses gasoline or diesel, and on the engine management system’s design.

• Check engine light illuminated on the dashboard
• Hard starting or extended cranking time
• Poor acceleration or hesitation
• Rough idle, especially when cold
• Decreased fuel efficiency
• In some diesel models: engine stalling or surging
• Difficulty in passing emissions tests

Probable Causes for DTC P0187 #

The most common causes for a P0187 code relate to issues with the sensor itself, wiring faults, or connector problems. Less frequently, the PCM or engine control unit (ECU) may be at fault. Identifying the root cause requires a systematic approach, as several issues can trigger this low-circuit condition.

1. Faulty fuel temperature sensor “B” (internal short or open circuit)
2. Damaged or corroded wiring between the sensor and the PCM
3. Poor electrical connection at the sensor or PCM connector
4. Short to ground in the sensor signal wire
5. Faulty PCM/ECU (rare, but possible)
6. Aftermarket modifications interfering with the fuel system wiring

Step-by-Step Diagnostics for P0187 #

Systematic diagnosis is essential for resolving P0187 efficiently. Skipping steps or guessing can lead to wasted time and unnecessary parts replacement. Always use a quality digital multimeter and follow OEM wiring diagrams for your specific vehicle model.

• Connect an OBD-II scanner and confirm P0187 is present. Check for related codes.
• Inspect the fuel temperature sensor “B” and its wiring for visible damage or corrosion.
• Disconnect the sensor. With the ignition off, check for bent, pushed out, or corroded pins in the connector.
• Using a multimeter, measure resistance across the sensor terminals. Compare to OEM specifications (typically in the range of several kilo-ohms at room temperature).
• Check for continuity and shorts between the sensor connector and the PCM using the wiring diagram.
• With the sensor disconnected, backprobe the harness connector and check for reference voltage (usually 5V) and ground.
• If wiring and connections are intact, replace the sensor and clear the code. Retest after a drive cycle.
• If the problem persists, perform advanced diagnostics on the PCM and related circuitry (best done by a qualified technician).

Possible Repairs for DTC P0187 #

Once you’ve pinpointed the cause of P0187, repair options will align with the identified fault. Precision is key: shotgun part replacement rarely solves the underlying issue. Always clear codes and perform a test drive to confirm that the repair was successful.

• Replace the faulty fuel temperature sensor “B”
• Repair or replace damaged wiring or connectors in the sensor circuit
• Clean corroded terminals and apply dielectric grease to prevent future issues
• Repair shorts to ground or open circuits as indicated by test results
• If necessary, replace or reprogram the PCM/ECU (rare and should be last resort)

Is It Safe to Drive with Code P0187? #

Driving with P0187 is possible but not recommended for extended periods. The engine may compensate for incorrect fuel temperature readings, but this can lead to performance loss, poor fuel economy, and—in rare cases—further damage to fuel system components. If you notice severe symptoms such as stalling, hesitation, or hard starting, it’s best to avoid driving until repairs are completed.

Vehicles Most Commonly Affected by P0187 #

While P0187 can appear on a wide range of vehicles, it is more frequently reported on models with advanced fuel management systems and multiple temperature sensors. Both gasoline and diesel vehicles can be affected.

• Ford F-Series (diesel and gasoline models)
• Chevrolet Silverado and GMC Sierra (especially Duramax diesels)
• Dodge Ram (Cummins and HEMI engines)
• Mercedes-Benz Sprinter (diesel variants)
• BMW diesel models (3 Series, 5 Series)
• Toyota Hilux and Land Cruiser (common rail diesel)
• Nissan Titan and Frontier (diesel and gasoline)

Common Mistakes & Best Practices for P0187 #

Misdiagnosis is frequent with P0187, often leading to unnecessary sensor or PCM replacement. Thorough testing and following the wiring diagram are vital. Here are some typical pitfalls and tips to ensure reliable repairs.

• Replacing the sensor without checking wiring—corroded or damaged wires are a common culprit.
• Ignoring related codes—other fuel system codes may point to a larger issue.
• Forgetting to clear codes and retest—always confirm the repair with a drive cycle.
• Skipping connector inspections—loose or dirty pins can cause intermittent faults.
• Use only OEM-specified replacement parts for sensors and connectors.

Quick FAQ for DTC P0187 #

Uncertain about next steps? Here are answers to some of the most common questions about this code:

• Can a bad fuel temperature sensor cause my car not to start?
  Yes, in some cases—especially on diesel engines—an out-of-range fuel temperature signal can cause hard starting or prevent the engine from starting altogether.
• Can I clean the fuel temperature sensor instead of replacing it?
  Usually, cleaning does not resolve sensor failures. If the sensor is faulty internally, replacement is the only reliable solution. However, cleaning corroded connectors can help restore proper function.
• Will a generic code reader clear P0187?
  Most OBD-II code readers can clear this code, but the underlying issue must be repaired or the code will return.