OBD-II Code · Sensors
P0179
Flex Fuel Composition Sensor High Input
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Flex fuel sensor voltage too high.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Cold start issues
Likely causes
- Failed sensorMost common
- Wiring short to power
Read the full diagnostic procedureP0179 is the high-input mirror of P0178 — the fuel composition sensor signal is above the upper threshold, typically a frequency >160 Hz or a stuck-h…
P0179 is the high-input mirror of P0178 — the fuel composition sensor signal is above the upper threshold, typically a frequency >160 Hz or a stuck-high voltage near reference. High input almost always means either the signal wire is shorted to the 5V reference or to battery voltage, or the sensor's internal output stage has failed open and is letting the pull-up resistor inside the ECU dominate the reading.
Workflow on a shop floor
- Disconnect the sensor connector and read the signal wire voltage at the ECU end with KOEO — if it stays pegged high with the sensor unplugged, the short is in the harness between the connector and the ECU; if it drops to zero or floats, the sensor itself is the fault.
- Check the connector pins for green corrosion or pushed-back terminals — a signal pin touching the 5V reference pin in a contaminated connector produces exactly this symptom.
- Confirm fuel-tank/sensor grounding — a missing or high-resistance ground at the sensor housing can elevate the signal reference and trigger high-input faults. The whole circuit-isolation test runs about 15 minutes with a DMM, and almost always points cleanly to either wiring or sensor without needing further teardown.
Vehicle-specific patterns2006-2011 GM trucks/SUVs FlexFuel commonly throw P0179 from a chafed harness where the signal wire shorts against the 5V reference at a frame-rail ab…
- 2006-2011GM trucks/SUVs FlexFuel commonly throw P0179 from a chafed harness where the signal wire shorts against the 5V reference at a frame-rail abrasion point — splice repair clears it.
- 2008-2012Ford F-150 / Expedition FlexFuel throws P0179 when the sensor's internal output transistor fails open, which Ford service has tracked on certain build dates with replacement coverage under emissions warranty for many years.
- 2007-2014Chevy Tahoe / Suburban FlexFuel will throw P0179 paired with P0178 on intermittent intervals when the connector is loose or corroded — same root cause, different snapshot of the same fault.
- 2009-2013Dodge Ram FlexFuel V8 throws P0179 less commonly but typically traces to a pinched harness where the fuel-tank skid plate was reinstalled improperly. Repair cost $150-$400 — clean a corroded connector at the low end, replace the sensor at the high end.
Look up another code
P0179 — frequently asked
What does a P0179 code mean?
Flex fuel sensor voltage too high.
What causes a P0179 code?
Common causes: Failed sensor; Wiring short to power.
What are the symptoms of a P0179 code?
Typical symptoms: Check engine light; Cold start issues.
Is it safe to drive with a P0179 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0179 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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