P2243
Sensor Reference Voltage Circuit/Open Bank 1 Sensor 1P2243 is a generic OBD-II powertrain diagnostic trouble code: Sensor Reference Voltage Circuit/Open Bank 1 Sensor 1. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2243 means
Code P2243 is set when the PCM detects that the reference voltage circuit for the upstream oxygen sensor on Bank 1 is open or has lost signal. This code is unique to vehicles using a wideband (broadband/linear) AFR sensor. Unlike a simple narrowband sensor, a wideband sensor contains a Nernst cell — a classical zirconia electrochemical element — that the ECU holds at a fixed internal reference voltage (typically 450 mV) by controlling the pumping cell current. A separate dedicated reference voltage wire carries a stable bias voltage from the ECU to the sensor, providing the stable electrical reference point the Nernst cell needs to operate. When this reference circuit is open or missing, the sensor cannot establish its internal operating point, and the entire lambda measurement system becomes non-functional.
With the reference circuit open, the PCM loses all closed-loop AFR feedback and enters open-loop mode. Fuel metering is governed solely by pre-programmed tables based on engine speed, load, and coolant temperature. This typically results in slightly rich fuelling (conservative open-loop maps), elevated emissions, and reduced fuel economy. The MIL illuminates and the vehicle will fail an OBD-II emissions inspection.
The reference circuit is a low-current, low-voltage line that is susceptible to corrosion and connector damage. An important and often overlooked failure mode is moisture intrusion through the sensor's wiring cover: on many sensor designs the boot/cover doubles as a vent port for the reference air channel. If the cover is cut, removed, or submerged, water can enter the sensor body and short or corrode the reference circuit internally, permanently damaging it.
Common causes
Most-frequently reported root causes when P2243 is logged.
-
1
Internal failure of the wideband sensor's reference voltage circuit — often caused by moisture intrusion through the sensor vent/boot (most common)
-
2
Open circuit in the reference voltage wire between the sensor connector and the PCM
-
3
Corroded, bent, or backed-out connector pins at the sensor harness plug
-
4
Damaged sensor wiring cover/boot allowing water into the sensor body
-
5
Chafed reference voltage wire contacting exhaust or chassis (short to ground or open)
-
6
Blown fuse or relay in the sensor supply circuit
-
7
Failed sensor heater causing condensation and internal cell damage
-
8
PCM internal reference voltage output failure (rare)
Symptoms drivers notice
How to diagnose P2243
A typical diagnostic flow when this code is present.
-
1
Connect a scan tool and retrieve all stored DTCs and freeze-frame data; note fuel trim values and whether companion sensor or heater codes are stored alongside P2243
-
2
Inspect the sensor boot/wiring cover carefully — if it is cut, missing, or has been submerged, water may have entered the sensor body and damaged the internal reference circuit
-
3
Visually inspect the full wiring harness from the sensor to the ECU for chafed insulation, heat damage, or connector corrosion
-
4
With the ignition off, test the reference voltage wire for continuity between the sensor connector and the PCM connector using a DVOM; an open reading (OL) confirms a broken circuit
-
5
Check for a short to ground on the reference wire; resistance to chassis ground should be infinite (OL)
-
6
With the ignition on (engine off), measure the reference voltage at the sensor connector using the PCM wiring diagram to identify the correct pin; compare to specification (typically ~5 V or a manufacturer-defined bias voltage)
-
7
If the circuit tests good but no reference voltage is present at the sensor pin, suspect a PCM output fault; if voltage is present but the code persists, replace the wideband O2 sensor
-
8
After repair, clear all DTCs and perform a complete OBD-II drive cycle to confirm readiness monitors reset without the fault recurring
Vehicles where we've handled P2243
Platforms in our catalogue with confirmed P2243 coverage.
Related powertrain codes
- B0001 — PCM Discrete Input Speed Signal Error
- B0004 — PCM Discrete Input Speed Signal Not Present
- C0359 — Four Wheel Drive Low Range (4LO) Discrete Output Circuit
- C0362 — 4LO Discrete Output Circuit High
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
Frequently asked questions
What is the reference voltage circuit on a wideband O2 sensor?
The reference voltage is a stable bias voltage the ECU supplies to the sensor's Nernst cell — the internal element that measures oxygen partial pressure in the exhaust.
Why is the sensor vent/boot so important with P2243?
Many wideband sensors use the wiring cover boot as both a protective sleeve and a vent channel that supplies reference air to the back side of the Nernst cell.
How is P2243 different from P2237 or P2238?
P2237 and P2238 relate to the pumping cell's positive current control circuit. P2243 involves the separate reference voltage circuit that biases the Nernst cell.
Can P2243 appear on vehicles with a standard narrowband O2 sensor?
No. A conventional narrowband zirconia sensor operates on a simple voltage output principle and does not have a separate reference voltage control circuit.
Will the engine still run with P2243 set?
Yes, but in open-loop mode only. The PCM will use fixed fuel maps without AFR feedback, typically running slightly rich.
Disabling P2243 in software
RaceTune can permanently disable P2243 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P2243 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C74 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P2243 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file