Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. P2040 OBD-II Trouble Code: Reductant Injection Air Pressure Sensor Circuit High Input

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

Check Engine Light

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?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...


Related questions

Q: Hello I have a 2006 f150 XLT with a 2v 4.6. It has a cold air intake from k

Hi, thanks for writing in. I'd be happy to help you. Code P2104 relates the throttle position control actuator, and code P2126 relates to the throttle position sensor. When either of these components is not working properly, this can cause...

Q: Fuel is leaking and Check Engine Light is on - 2008 Mazda 3

The fuel pump is contained within the tank and so cannot leak. You are probably seeing fuel leaking from a fuel line and/or from the fuel tank itself. There could be a loose fuel line fitting, impact damage (debris from...

Q: My truck runs for about 20 minutes and then dies. After few minutes starts back up. Changed fuel pump and few other things

Try cleaning the mass air flow sensor as these sometimes get dirty which can cause it to not run well or at all in some cases. Without additional detail as to what else has been changed, it is tough to...