P0186Generic code

P0186 Code: Fuel Temperature Sensor B Circuit Range/Performance

The P0186 code means the fuel temperature sensor B reading is electrically valid but does not agree with the other sensors. It is usually a sensor that reads wrong or gets stuck, although it can also be a real abnormal condition in the engine. After the vehicle has sat, sensor B should match sensor A.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$40 to $300
Difficulty
Medium
System
Fuel Injection
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0186 code means

Fuel temperature sensor B is the second measuring point in the fuel system (depending on the manufacturer, another section of the rail, the return line or the second tank). The computer uses it because it complements the sensor A reading, which lets it correct injection and protect the system.

Here the signal is within the electrical limits, but it is not believable. The computer compares the fuel temperature sensor B with other data: after the vehicle has sat for several hours, it should match sensor A and the ambient temperature. If the difference is larger than allowed for the programmed time, it sets the P0186 code. This is not a cut wire. It is a sensor that reads wrong, freezes at one value or reacts too slowly, or else a real abnormal condition.

Keep in mind that the code points to the circuit where the computer saw the problem, not necessarily the part that failed. Check the wiring before you replace the sensor, and treat the P0186 code as a starting point for testing rather than a parts list.

P0186 code symptoms

  • Check engine light on and steady.
  • In many cases you notice nothing while driving, only the light on the dash.
  • Possible companion codes from the same sensor (low, high or intermittent signal).

Likely causes of the P0186 code

  1. Sensor out of calibration or worn, giving a believable but wrong value.
  2. A real abnormal condition. The system really is working outside normal limits.
  3. Dirty sensor or one with deposits, which makes it respond slowly.
  4. High resistance in the connector from corrosion, which shifts the reading.
  5. Computer software. Some manufacturers have released updates for false range codes.
  6. Also check: Look in the service manual to see which sensor is B on your engine, because the assignment changes between manufacturers.

How to diagnose the P0186 code step by step

  1. Read the live data from the sensor and compare it with what you expect. After the vehicle has sat for several hours, it should match sensor A and the ambient temperature.
  2. Inspect the connector. Unplug it, look for green, backed-out or oily pins, and plug it back in firmly.
  3. With the key on and the sensor unplugged, measure the reference at the connector. You should see about 5 V between the signal pin and ground.
  4. Do the jumper test. With the sensor unplugged, the scan tool should show about -40 °C (-40 °F). When you join the two connector pins with a jumper wire, the reading should jump to over 120 °C (248 °F). If it does, the wiring is good and the problem is the sensor.
  5. Measure the sensor resistance and compare it with the technical data table at the current temperature.
  6. Do a wiggle test. With the engine running, move the harness and the connector while you watch the live data. A sudden jump gives away the spot where the fault is.
  7. Check the continuity of each wire between the sensor connector and the computer connector with the key off.

How to fix the P0186 code

  • Correct the real condition if there is one (thermostat, level, leaks, fuel).
  • If the sensor reads wrong against a reference thermometer or gauge, replace it.
  • Look for technical service bulletins or software updates from the manufacturer.
  • Use a quality OE or equivalent sensor. Cheap generic ones often have different response curves.
  • Clear the codes, drive a full drive cycle and check in the live data that the reading makes sense.

Technical reference data

  • Two-wire NTC thermistor with a 5 V reference.
  • Approximate resistance: 2,000 to 3,000 ohms at 20 °C (68 °F).
  • Open circuit: about -40 °C (-40 °F). Short circuit: over 120 °C (248 °F).
  • These are approximate values. Check the manufacturer data for your engine.

Brand-specific notes

This is an uncommon code. It shows up mostly on diesels and on vehicles with two fuel tanks.

If you cannot find sensor B on your engine, check the manufacturer information before you buy any parts.

Frequently asked questions about P0186

What does the P0186 code mean?
The P0186 code means the fuel temperature sensor B signal is electrically valid but does not agree with the other sensors. Usually the sensor reads wrong or is stuck at one value, although it can also be a real abnormal condition in the engine.
Can I drive with a P0186 code?
Yes, in general there is no immediate risk. The engine runs on a substitute value and may use a bit more fuel, so get it repaired soon.
What is the most common cause of P0186?
The most common cause is a sensor that has drifted or gone slow and now gives a believable but wrong value. A real abnormal condition in the engine can also trigger it, and so can corrosion that adds resistance in the connector.
Does the P0186 code always mean I need a new fuel temperature sensor B?
No. In most cases the fault is in the connector or the wiring. Do the supply, ground and continuity tests first, and replace the sensor only when those pass.
What is the difference between a low signal and a high signal?
On a thermistor, a low signal means an impossibly high temperature (a short), and a high signal means an impossibly low temperature (an open circuit).
How much does it cost to fix P0186?
Roughly $40 to $300. The cheap end is repairing a connector, and the expensive end is replacing the sensor with labor. Prices vary by region and shop.
Will a P0186 code clear itself?
Not on its own. If the cause was a loose connector that you have fixed, the code will not come back, but if the fault is still there the computer sets P0186 again. Clearing it with a scan tool without finding the cause only hides it for a while.

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