P0188Generic code

P0188 Code: Fuel Temperature Sensor B Circuit High

The P0188 code means the fuel temperature sensor B signal is above its maximum value. On a thermistor that reads as an impossibly cold temperature, almost always from an open circuit or a loose connector. Check the connector first.

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 P0188 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.

The sensor is an NTC thermistor fed with 5 V by the computer. A signal close to 5 V is the same as an impossibly low temperature (the scan tool usually shows -40 °C, or -40 °F), which almost always means an open circuit: a loose connector, a cut wire, a broken sensor ground or a sensor that is open inside. While the fault lasts, the computer believes the fuel is very cold, so it loses an injection correction. That is what sets the P0188 code.

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 P0188 code as a starting point for testing rather than a parts list.

P0188 code symptoms

  • Check engine light on and steady.
  • The computer thinks the fuel is very cold and loses an injection correction.
  • 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 P0188 code

  1. Unplugged or poorly seated connector, for example after a repair or after changing the air filter.
  2. Signal or ground wire cut inside the insulation or at the connector itself.
  3. Corroded or open connector pins that no longer make contact.
  4. Sensor open inside, with infinite resistance.
  5. 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 P0188 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 P0188 code

  • If the connector was loose or corroded, clean it with contact cleaner and secure it.
  • If the jumper test shows the wiring is good, replace the sensor.
  • If the signal is missing at the connector, repair the open wire by soldering it and sealing it with heat shrink.
  • 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 P0188

What does the P0188 code mean?
The P0188 code means the fuel temperature sensor B signal is above its maximum value. On a thermistor that reads as an impossibly cold temperature, and it almost always comes from an open circuit or a loose connector.
Can I drive with a P0188 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 P0188?
The most common cause is a loose, unplugged or corroded connector, followed by a cut signal or ground wire. A sensor that has gone open inside is less likely.
Does the P0188 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 P0188?
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 P0188 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 P0188 again. Clearing it with a scan tool without finding the cause only hides it for a while.

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