A fuel temperature reading should rise and fall slowly. When the second sensor’s reading flickers between normal and extreme values, the cause is in the circuit, not the fuel. A P0189 code means the engine computer caught the fuel temperature sensor “B” signal dropping out or jumping for brief moments.
This guide explains what causes intermittent faults, how to recreate them and which repairs stop them.
P0189 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 1 | Fuel and air metering | The fault involves the sensors that measure air and fuel. |
| 89 | Specific fault | Fuel Temperature Sensor B Circuit Intermittent |
What the P0189 Code Means
The SAE J2012 standard defines the P0189 code as Fuel Temperature Sensor B Circuit Intermittent. Sensor B is the second fuel temperature sensor on vehicles that use two.
The powertrain control module (PCM) expects fuel temperature to change gradually. When sensor B jumps to -40°F or to an extreme hot value and then returns to normal in a split second, the PCM knows the circuit lost contact or shorted briefly. It then sets the code.
The glitch may be over before you can see it. That is why the sensor often tests fine in the driveway.
Symptoms of an Intermittent Sensor B Signal
Symptoms of a P0189 code appear only while the signal acts up. Look for these signs:
- Check engine light that comes and goes
- Fuel temperature B jumping on the scan tool
- Brief power loss on some diesels
- Occasional stumble or hard start
- Problems that show up over bumps
What Causes the P0189 Code?
Anything that breaks the circuit for a moment can set this code. These are the common causes:
- Loose connector. A connector that is not fully locked loses contact with vibration.
- Spread or corroded terminals. Weak pins lose their grip.
- Chafed wiring. Wires rubbing on brackets can short or open briefly.
- Broken wire inside the insulation. The copper separates only when it flexes.
- Failing sensor B. A cracked thermistor can lose contact as it heats.
- Fuel or water in the connector. Contamination causes brief shorts.
How to Track Down the P0189 Code
A scan tool that can graph live data is the most useful tool. The goal is to make the glitch happen while you watch.
Read Freeze Frame Data
Check the freeze frame data stored with the code. It shows engine speed, load and temperatures when the fault set. Try to recreate those conditions on a test drive while you graph both fuel temperature sensors.
Do a Wiggle Test
With the engine idling, graph fuel temperature B. Gently wiggle the connector, then the wiring, one short section at a time. A sudden spike or drop marks the bad spot. Tap the sensor body lightly too, since an internal crack may react to vibration.
Inspect the Connector
Unplug the connector and look for corrosion, spread terminals, fuel residue and a broken lock. Sensors near the fuel filter or pump often collect fuel and dirt around their connectors.
Repairs That Fix the Fault
Fix the problem you found, clear the code and drive under the same conditions that set it.
- Reseat and lock the connector until the tab clicks.
- Clean the terminals and add dielectric grease to the seal.
- Replace worn terminals or the pigtail when pins no longer grip.
- Repair damaged wiring with solder and heat shrink tubing.
- Replace sensor B if it reacts to tapping.
Relieve fuel pressure before removing the sensor, and follow the service manual on diesel or direct injection systems.
Once you find the bad spot, check nearby wiring too. Heat and vibration that damaged one section often affect the wiring around it. Replacing a short length of damaged wiring now can stop the next glitch before it starts.
Repair Cost Breakdown
Finding the cause of a P0189 code often takes more time than fixing it. This table shows typical ranges.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Connector cleaning | $10 to $15 | $50 to $100 |
| Terminal or pigtail replacement | $15 to $40 | $100 to $200 |
| Wiring repair | $10 to $30 | $100 to $300 |
| Fuel temperature sensor B | $20 to $120 | $100 to $300 |
| Diagnostic time | Free with your own tools | $100 to $200 |
Is It Safe to Drive with a P0189 Code?
You can usually drive carefully. Short glitches may cause a stumble or a moment of reduced power on some diesels.
Intermittent faults often get worse until they fail completely. Fix the problem while it still shows up on a wiggle test.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0184 | Fuel Temperature Sensor A Circuit Intermittent |
| P0185 | Fuel Temperature Sensor B Circuit Malfunction |
| P0186 | Fuel Temperature Sensor B Circuit Range/Performance |
| P0187 | Fuel Temperature Sensor B Circuit Low Input |
| P0188 | Fuel Temperature Sensor B Circuit High Input |
Stopping an Intermittent Sensor B Signal
A P0189 code means fuel temperature sensor B drops out or jumps for short moments. Loose connectors, damaged wires and failing sensors cause most cases.
- Use freeze frame data to recreate the fault.
- Graph the signal while you wiggle the wiring.
- Inspect the connector for corrosion and fuel residue.
- Replace the sensor only after the wiring checks out.
Frequently Asked Questions
Why Is an Intermittent Fault Hard to Find?
The fault may happen only with heat, vibration or moisture, and only for a split second. When you test the parked vehicle, everything may look normal. Graphing the signal while you wiggle the wiring is the best way to catch it.
Can I Ignore the P0189 Code?
It is not a good idea. The glitches can cause stumbles or brief power loss, and the fault often grows into a constant failure. Fixing a loose pin now is cheaper than chasing a bigger problem later.
Why Does the Code Show Up in Wet Weather?
Water can get into a connector with a worn seal. It creates brief shorts between the pins, which make the reading jump. If the code appears mostly in rain or after washing the vehicle, focus on the connector seal.
Is the P0189 Code Related to P0184?
They are the same type of fault on different sensors. P0184 is an intermittent fault on sensor A, while the P0189 code is the same problem on sensor B. If both appear, look for a shared connector or ground.
Can a Bad Ground Cause the P0189 Code?
Yes. A loose or corroded engine ground strap can make several sensor signals flicker at once. If other sensor codes come and go at the same time as this one, clean and tighten the ground straps before replacing any sensors.