P2040 OBD-II Trouble Code: Reductant Injection Air Pressure Sensor Circuit High Input

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Cost of diagnosing the P2040 code

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 is on diagnostic inspection. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

P2040 code definition

Reductant Injection Air Pressure Sensor Circuit High Input*

*Definition could differ depending on manufacturer code usage, for example, “Oil Quality Sensor ME-SFI” (Mercedes)

What the P2040 code means

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.

What causes the P2040 code?

  • 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.

What are the symptoms of the P2040 code?

  • The Check Engine Light will not be illuminated, and the code is set in ECM memory as a oil quality fault.

How does a mechanic diagnose the P2040 code?

  • 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

Common mistakes when diagnosing the P2040 code

  • Clearing ECM memory codes before checking the oil sensor data in memory
  • Failing to clear ECM codes after the P2040 codes are fixed

How serious is the P2040 code?

  • 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.

What repairs can fix the P2040 code?

Additional comments for consideration regarding the P2040 code

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.

Need help with a P2040 code?

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Nazareth

26 years of experience
168 reviews
Nazareth
26 years of experience
Mercedes-Benz CLA250 - Check Engine Light is on - Los Angeles, California
Polite and very professional! Nazareth quickly identified my car was suffering from low voltage issues and the battery was the problem. The reader was showing 8 volts hence why my car didn’t receive enough power to start, it needed 12v. My battery was 4 years old and never been changed. Thank you Nazareth!

Cornelius

17 years of experience
78 reviews
Cornelius
17 years of experience
Chevrolet Cobalt - Check Engine Light is on - Peachtree City, Georgia
He was very helpful with explaining what could lead to my check engine light being on. And helping clear my engine light.

Marco

28 years of experience
78 reviews
Marco
28 years of experience
Nissan Maxima - Check Engine Light is on - Highland, California
Marco did a great job of finding the source of the problem and his recommendations were greatly appreciated.

Juan

8 years of experience
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Juan
8 years of experience
Chevrolet Tahoe - Check Engine Light is on - Altamonte Springs, Florida
Juan was on time for both appointments. He was knowledgeable and polite and I will most definitely be requesting him for my next steps based on the quote he provided me for other issues I need to address. Excellent customer service and top notch repair work!


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