P2591
Reductant Level Sensor Circuit HighP2591 is a generic OBD-II powertrain diagnostic trouble code: Reductant Level Sensor Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2591 means
P2591 is triggered when the ECM receives a signal from the reductant level sensor that is above the expected maximum voltage threshold for the circuit. This high-circuit condition prevents the module from accurately determining how much DEF remains in the tank, which is critical for SCR system management and for alerting the driver before the tank runs dry.
The most common cause is a short to voltage in the signal wire between the sensor and the ECM, or an internal failure within the level sensor assembly itself. Moisture intrusion into the DEF tank module connector is also frequently seen because of the corrosive nature of urea solution. A failed ECM input circuit can produce the same code but is a much less common cause.
While the SCR system may continue to dose reductant if the fault is present in isolation, the module will not be able to warn the driver of a low DEF condition. Running the tank dry can introduce air into the reductant pump and lines, leading to additional faults and potentially requiring a priming procedure before the system resumes normal operation.
Common causes
Most-frequently reported root causes when P2591 is logged.
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1
Short to voltage on the reductant level sensor signal wire.
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2
Failed level sensor assembly with internal signal short.
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3
Moisture or urea contamination in the DEF tank module connector causing pin-to-pin bridging.
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4
Damaged wiring harness with chafed insulation contacting a voltage source.
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5
Faulty ECM input circuit holding the signal line high.
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6
Incorrect replacement sensor with wrong resistance or voltage range.
Symptoms drivers notice
How to diagnose P2591
A typical diagnostic flow when this code is present.
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1
Connect scan tool, record DTCs and check live DEF level sensor PID value.
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2
Inspect the DEF tank module connector for urea crystal deposits, corrosion, or moisture.
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3
Disconnect the sensor connector and measure signal wire voltage; voltage present with connector unplugged confirms a short to voltage in the harness.
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4
Measure sensor resistance or voltage output at the sensor connector per specification.
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5
Inspect wiring harness routing from tank module to ECM for damage.
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6
Repair wiring short or replace the DEF tank level sensor module as needed.
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7
Clear DTCs and confirm sensor PID reads plausible values across the expected range.
Vehicles where we've handled P2591
Platforms in our catalogue with confirmed P2591 coverage.
Related powertrain codes
Frequently asked questions
Will P2591 prevent me from filling the DEF tank?
No, the fault does not lock the fill port; however, because the sensor is unreliable, you should maintain a full tank until the fault is repaired to avoid running dry.
Can urea corrosion cause this fault?
Yes, DEF is mildly corrosive to certain metals; connector pins corroded by urea contact can create resistive shorts that drive the signal wire high.
Is P2591 the same as P2590?
P2590 is the low circuit variant; P2591 is specifically a high circuit fault. Both prevent accurate level measurement but point to opposite electrical failure modes.
Does this code immediately trigger a derate?
Not usually on the first drive cycle; most manufacturers implement a multi-cycle inducement strategy, but the MIL will be on and the root cause should be addressed promptly.
Disabling P2591 in software
RaceTune can permanently disable P2591 — 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 P2591 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 EDC17C50 verified 1 software version
- Bosch EDC17C56 verified 1 software version
- Bosch MD1CP002 verified 1 software version
- Bosch MD1CS001 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 P2591 in your scan?
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