OBD-II Code
P2243
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$40–$800
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P2243 means the ECM has lost the 5V reference voltage feeding the wideband (air/fuel ratio) sensor on bank 1 sensor 1 — the upstream sensor that drives the fuel-trim loop.
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 follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
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
Read the full diagnostic procedureP2243 means the ECM has lost the 5V reference voltage feeding the wideband (air/fuel ratio) sensor on bank 1 sensor 1 — the upstream sensor that driv…
P2243 means the ECM has lost the 5V reference voltage feeding the wideband (air/fuel ratio) sensor on bank 1 sensor 1 — the upstream sensor that drives the fuel-trim loop. Modern wideband sensors are not the simple narrowband switching sensors that throw P0130-series codes; they require a regulated 5V reference (the same VREF rail that often feeds the MAP, TPS, and pedal-position sensors) plus a heater circuit and a pump-current return. When P2243 sets, it usually means the VREF leg is open, shorted to ground, or drooping below spec — not that the sensor element itself is dead.
Cheapest-first ladder
- back-probe the 5V VREF pin at the upstream O2 connector key-on-engine-off, must read 4.9-5.1V steady; anything below 4.5V or above 5.3V is a regulator or shared-circuit fault, anything reading 0V is an open circuit between the ECM and the connector.
- Check the harness ground reference at the same connector (under 0.1V drop to battery negative).
- Wiggle-test the engine harness with the scanner connected and the freeze-frame loaded — most P2243 calls in shop work trace to a chafed or corroded splice in the engine-harness branch, not the sensor itself.
- If VREF is in spec at the connector but the sensor's signal still reports open, swap in a known-good sensor before condemning the ECM. Before condemning the wideband sensor on a P2243, ALWAYS verify the 5V reference at the connector — replacing a $250-$450 wideband sensor on a vehicle that actually has a chafed VREF wire or a failed ECM driver just sets the code again on the next drive cycle.
Vehicle-specific patterns2010-2016 Ford 3.5L EcoBoost (F-150, Flex, Taurus SHO, Explorer Sport) is the dominant P2243 platform in shop work — a known engine-harness chafe poi…
- 2010-2016Ford 3.5L EcoBoost (F-150, Flex, Taurus SHO, Explorer Sport) is the dominant P2243 platform in shop work — a known engine-harness chafe point at the engine-harness-to-bulkhead connector corrodes the shared 5V VREF, and Ford issued a TSB covering harness inspection and repair on early 3.5 EB VINs; check service-history coverage before quoting a sensor.
- 2012-2018Ford 2.7L EcoBoost shares the same harness-family weakness.
- 2008-2014Subaru EJ255/EJ257 (WRX, Forester XT, Legacy GT) throws P2243 from a brittle wideband connector at the up-pipe where exhaust heat cooks the harness insulation.
- 2007-2013BMW N54/N55 (335i, 535i, X3 35i) throws P2243 from a failed DME 5V driver on high-mileage cars — the same VREF rail also feeds the MAP, so a P2243 paired with P0107/P0108 points at the DME, not the O2.
- 2005-2010Mazda Speed3/Speed6 with the MZR DISI turbo throws P2243 from the wideband controller module-internal failure.
Estimated repair$40 to $800.
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