P0839: Four Wheel Drive (4WD) Switch Circuit High
What to do
Drive mode selection may be unavailable. Worth having the underfloor connectors inspected rather than only the dashboard switch — corrosion there is common and looks like a failed switch from inside the car.
What this code means
The four-wheel-drive switch circuit reads above its valid range — an open circuit or a short to supply. A corroded underfloor connector produces the same reading as a broken wire and is the more likely of the two on a vehicle that has spent winters on salted roads.
Likely causes
Start here
- Open circuit in switch wiring · moderate
- Corroded or loose connector · easy
- Faulty four wheel drive switch · easy
Less common
- Road damage to underfloor wiring · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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