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P2040 is a diagnostic trouble code (DTC) for "Reductant Injection Air Pressure Sensor Circuit High Input". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $154.99 . Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $50.0 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
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Reductant Injection Air Pressure Sensor Circuit High Input*
*Definition could differ depending on manufacturer code usage, for example, “Oil Quality Sensor ME-SFI” (Mercedes)
P2040 is an OBD-II generic code for the Reductant Injection Air Pressure Sensor Circuit High Input. However, the code is used by manufacturers at their discretion, and they can change the usage of the code to whatever they want. Since this code definition is not used by most manufactures, some, such as Mercedes, are using it for another failure.
Mercedes uses P2040 as an oil quality sensor ME-SFI code for the oil quality signal being implausible, not credible, or out of specified duty cycle range of smaller than 17% to larger than 83%, while checking the oil dielectric content for excess water in the oil.
The Engine Control Module (ECM) monitors the engine oil quality sensor duty cycle and detects a reading to be below 17% or above 83% (Mercedes)
The dielectric reading goes above 5.8 dielectric sensor output to the ECM (indicates the oil contains excessive water*)
*Normal readings from the sensor for oil without water would be between 2.3 and 4.0.
Scans codes and documents the code in the ECM
Scans for codes other than P2040 in the ECM and diagnoses those codes as per the manufacturer's pinpoint test
Clears the ECM code P2040 after engine oil and filter change
Rescans the ECM oil sensor for a reading to below 4.0 dielectric
Code P2040 is an indication that the engine oil has too much water moisture content in the oil.
The excess water in the oil could lead to lack of lubrication to the bearings and engine component failure if the engine is run for a long time with excessive water in the oil without an oil change.
Replacing the oil sensor if the oil quality readings do not change after the oil and filter is changed
Code P2040 is used mostly by manufacturers with diesel engine oil quality sensors and not for the OBD-II generic code description Reductant Injection Air Pressure Sensor Circuit High Input.
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