P0186: The engine computer sees fuel temperature sensor B giving a reading outside the normal range or not behaving as expected.
Fuel temperature sensor B reading out of range
Severity: Severity not verified — if the car runs badly, have it inspected
The sources describe the code and its causes but do not say how urgent it is. The usual symptoms are a check engine light and some loss of fuel economy, so have it read and checked rather than ignored.
P0186 in short
P0186 means the signal from fuel temperature sensor B is outside the normal range, on vehicles that have a second fuel temperature sensor. The computer needs fuel temperature to estimate fuel density. Wiring or connector faults are the usual cause, then the sensor itself, and rarely the computer.
Fuel gets less dense as it warms, so the computer uses the fuel temperature reading to fine tune injection. When sensor B gives a value outside the range it expects, P0186 is set.
TroubleCodes.net lists water, corrosion or harness damage first, a failed sensor less often, and a computer fault rarely.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Wiring or connector fault in the B circuit
Common general cause- Why it ranks here
- A reading outside the normal range is most often a wiring or connector problem, which TroubleCodes.net lists ahead of the sensor.
- What would change this
- Rises if the connector is corroded or the reading jumps when the harness is moved. Falls if wiring and connectors test normal.
Cause 2: Failed temperature sensor
Common general cause- Why it ranks here
- TroubleCodes.net lists the sensor itself as a possible cause, though less common than the wiring.
- What would change this
- Rises if the circuit tests good and the sensor resistance is outside the manual figures. Falls if the resistance is correct.
Cause 3: Engine computer fault (rare)
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists the computer as a rare cause, often after water or collision damage.
- What would change this
- Rises only after wiring and sensor test good. Falls if either is faulty.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all stored codes and freeze-frame data and note the fuel temperature readings if the scan tool shows them.
IfOther codes are stored with it
It meansSort out the other codes first, since a shared wiring or power fault can set several.
IfP0186 is the only code
It meansMove on to the connector and wiring checks.
Step 2: Inspect the sensor B connector and ECM connector for corrosion or water, and shake the harness while watching the reading.
Warning:Do not disconnect fuel lines or work near sparks. Turn the ignition off before unplugging connectors.
IfA damaged, corroded or loose connection is found, or the reading jumps when the harness moves
It meansThe wiring or connector is the likely cause.
IfWiring and connectors look and test normal
It meansTest the sensor and its reference voltage next.
Step 3: Check 5 volts reference and compare sensor resistance with the repair manual figures.
Warning:Back-probing can short pins and damage the computer. Follow a wiring diagram.
IfVoltage, resistance or continuity is outside the repair manual figures
It meansThe wiring or the sensor is at fault, so repair the wiring or replace the sensor.
IfEverything tests normal
It meansThe fault may be intermittent or in the computer, so have a shop retest.
Symptoms
- Check engine light on
- Poorer fuel economy
- Hard starting or reduced performance, in some cases
How to fix
Step 1: With the ignition off, look at the visible wiring and connector for the sensor for damage or corrosion.
Step 2: Ask a dealer or shop to check the circuit before buying a sensor for P0186.
On your vehicle
We don't have reviewed vehicle-specific evidence for P0186 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0186 yet.
P0186 questions
Is it safe to drive with P0186?
The sources list a check engine light and poorer fuel economy as the usual signs, but they do not rate urgency. Have it read and checked soon.
Sources and review
- P0186 - Fuel temperature sensor B circuit range/performance
- On-Board Diagnostic Trouble Codes (generic code title list)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error