P0185 — Fuel Temperature Sensor « B » Circuit

OBD-II trouble code P0185

Fast Facts:

  • System affected: Fuel system / Fuel temperature sensor
  • Severity: Moderate
  • Main symptoms: Engine warning light, possible poor fuel economy, initial rough running
  • Driveability: Limited / No (depending on other factors)

Manufacturer variations for trouble code P0185

Different vehicle manufacturers may label or code this fault somewhat differently, but the underlying issue remains the same — an issue with the Fuel Temperature Sensor « B » circuit. Below are some known variations:

  • Volkswagen / Audi / Skoda / SEAT: P0185 or P129A (depending on the specific model and software version)
  • Ford: P0185, sometimes listed under Fuel System or Sensor-specific fault codes
  • Peugeot / Citroën: P0185, often linked to fuel sensor or temperature sensor circuits
  • BMW / Mini: P0185, may be combined with other fuel sensor codes

What does trouble code P0185 mean?

To understand P0185, it’s important to know that modern vehicles rely heavily on sensors to provide real-time data to the ECU. The Fuel Temperature Sensor « B » specifically measures the temperature of the fuel within the fuel system, often in the tank or along the fuel line. This sensor’s data helps optimize fuel injection, mixture, and ignition timing, especially during cold starts or when fuel temperatures fluctuate.

The ECU monitors the electrical circuit of this sensor for consistency, voltage signals, and proper grounding. If it detects a fault — such as an open circuit, short circuit, or abnormal sensor readings — it sets the P0185 trouble code. Typically, the “B” suffix indicates that this is the second or auxiliary fuel temperature sensor, as some vehicles have multiple sensors for different parts of the system.

This fault often appears in scenarios like after replacing or repairing fuel system components, during cold weather, or if wiring issues develop over time. It might also appear if the sensor itself malfunctions or if there’s a problem with the ECU’s inputs.

Severity and risks of trouble code P0185

P0185

The main risks include:

  • Reduced fuel economy due to incorrect fuel temperature readings
  • Possible rough running, especially during cold starts
  • Increased emissions because of improper fuel mixture calculations
  • Potential for further sensor or wiring-related damage if ignored

**Can the vehicle be driven?** — Yes, but it is advisable to address the fault promptly to prevent long-term engine performance issues or damage.

Symptoms of trouble code P0185

While not all drivers experience overt symptoms, common signs include subtle engine performance issues or warning lights. Recognising these symptoms early can prevent further damage and costly repairs.

  • Illuminated check engine light on the dashboard
  • Inconsistent or rough engine idling
  • Decreased fuel efficiency
  • Engine stalls or hesitation during acceleration
  • Difficulty starting the engine, especially in cold conditions
  • Possible increase in emissions

Most likely causes of trouble code P0185

This fault usually results from issues related to the fuel temperature sensor circuit, wiring, or the sensor itself. Here are the most common causes, ranked from most to least likely:

  1. Faulty Fuel Temperature Sensor « B »: The sensor may have failed internally or due to age and exposure to fuel contaminants.
  2. Damaged or loose wiring and connectors: Corrosion, wear, or disconnection in the sensor’s wiring harness can disrupt signals.
  3. Short circuit or open circuit in the sensor wiring: Electrical faults caused by damaged wiring or connector pins.
  4. ECU or wiring harness issues: Less commonly, the problem is with the ECU input circuit itself.
  5. Fuel system contamination or damage: In rare cases, fuel or sensor contact issues may cause erratic readings.

How to diagnose trouble code P0185

Diagnosing this fault involves a systematic approach to verify the sensor, wiring, and ECU input. Always start with visual inspections before using diagnostic tools.

  1. Visual inspection: Check the wiring harness, connector pins, and sensor for corrosion, damage, or disconnection.
  2. Check live data: Using an OBD-II scanner, monitor the Fuel Temperature Sensor « B » values while the engine operates. Look for abnormal or inconsistent readings.
  3. Test wiring continuity: Use a multimeter to verify proper continuity and resistance in the wiring between the sensor and the ECU.
  4. Sensor testing: Measure the sensor’s resistance against manufacturer specifications if available, or replace the sensor to confirm diagnosis.
  5. Inspect related components: Examine the fuel system and associated wiring for damage or contamination.

Possible repairs for trouble code P0185

Depending on the root cause identified during diagnosis, repairs can vary from simple to complex. Below are typical corrective actions:

  • Replace the Fuel Temperature Sensor « B »: Basic repair requiring replacing the sensor, suitable for modern or age-related sensor failure.
  • Repair or replace damaged wiring and connectors: Professional work involving fixing wiring harness issues or cleaning corrosion.
  • Verify and repair ECU connections if needed: Only if wiring and sensor are intact, and issues persist, involving specialised diagnostics.
  • Fuel system inspection: In case of contamination, draining and cleaning the fuel system may be necessary; this is typically a professional repair.

Vehicles commonly associated with trouble code P0185 in Europe

Naturally, this issue can affect any vehicle equipped with the relevant sensors, but some models are more frequently reported in connection with P0185.

European vehicles with known common associations include:

  • Volkswagen Group: Golf, Passat, Tiguan (various engine families)
  • Ford: Focus, Fiesta, Mondeo (with petrol engines)
  • Peugeot / Citroën: 208, 308, C4, C5
  • BMW / Mini: 1 Series, 3 Series, Mini Cooper

Frequent mistakes with trouble code P0185

Diagnosing and repairing P0185 requires attention to detail. Common errors can lead to misdiagnosis or unnecessary repairs.

  • Replacing the sensor without proper testing: Replacing parts blindly can be costly; always verify the fault first.
  • Ignoring wiring and connection issues: Electrical faults are often overlooked but are the root cause in many cases.
  • Not clearing codes after repair: Failing to clear the fault code properly may result in the code returning without addressing the root issue.
  • Ignoring other codes or symptoms: P0185 may co-exist with other faults, requiring comprehensive diagnostics.

FAQ — trouble code P0185

Can this code disappear on its own? Yes, but it’s unlikely unless the fault was a temporary wiring glitch or sensor anomaly. Always diagnose to confirm.

Can I keep driving? Usually, yes. But if the engine runs rough or the check engine light is on, it’s best to repair the fault promptly. Continued driving might cause further damage or increased emissions.

Why does the code return after clearing? This usually indicates an unresolved electrical issue, faulty sensor, or wiring problem that needs attention before the code can be permanently cleared.

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