Fix P2201: Mechanic’s solutions that WORKED

The code P2201: NOx Sensor Circuit Range/Performance Bank 1 points out a fault in the NOx sensor circuit, specifically in Bank 1, and most likely is caused by a faulty sensor, incorrect DEF fluid, or other related emission system issues. This code triggers when the NOx sensor’s readings are out of the expected range, indicating potential problems with the vehicle’s emissions control system.

P2201 quick overview

Meaning	P2201: NOx Sensor Circuit Range/Performance Bank 1
Is it serious?	This code can be serious as it often relates to the vehicle’s emissions system, which can affect overall performance and compliance with emission standards.
Possible causes	– Faulty NOx sensor – Incorrect DEF fluid or contamination – Wiring or electrical issues in the NOx sensor circuit – Faulty EGR system components – Damaged exhaust or intake system causing incorrect readings
How to diagnose?	Check NOx Sensor Circuit: Use wiring diagrams to diagnose and inspect the NOx sensor circuit. Inspect NOx Sensor: Look for signs of damage or contamination on the NOx sensor. Verify DEF Quality: Ensure the Diesel Exhaust Fluid is correct and not contaminated. Consult Dealer or Specialist: Consider consulting with a dealer or specialist for warranty and advanced diagnostics. Inspect Related Components: Check the EGR system, exhaust, and intake for any signs of issues that could affect sensor readings.

How to fix P2201 – learn from mechanics

I looked into P2201 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle Information:
2013 Ford F-550 Super Duty XL 6.7L, MIL Lamp on

Issue + Repair History:

• Engine light on with code p2201.
• NOx reads around 100 ppm at a stop and over 300 ppm on hard acceleration.
• Freeze frame for code was at idle, no PID for NOx number.
• Replaced NOx module and sensor 1000 miles ago for code p2201.

Other OBD2 Codes + Test Results:

• P2201 – NOx sensor circuit range/performance.
• Load test powers and grounds showed good, bright headlamp bulb.
• Tested resistance of CAN from NOx module to PCM: 0.8 ohms.

Suggestions to Fix Issue:

• Check for a cracked DPF which might contaminate the NOx sensor with soot.
• Inspect for conditions causing lower than expected NOx, like EGR sticking open or exhaust leak.
• Look for usual issues like defective NOx sensor, dirty sensor pickup, damaged wiring, internal ECM issue, or connector problem.
• Consider the possibility of intake or exhaust leaks, and check the EBP and MAP for carbon build-up.
• Investigate EGR temperature, cooler temps, bypass valve operation, and secondary cooling system operation.
• Explore if there’s a related emission recall like in similar models from other manufacturers.

Final Fix:

• The mechanic replaced the EGR valve after finding the old one dirty and sticking open. The truck has been functioning well for 2 weeks since the repair.

Case #2: Ram

Vehicle Information:
2013 Ram 5500 ST 6.7L, MIL Lamp on

Issue + Repair History:

• Persistent codes: P2201, P229F, P20EE, new P207F after TSB reflash.
• Original codes: P2201, P229F, P20EE, P249E, P1C54 (last 2 resolved after reflash).
• Installed 2 new NOx modules, cleared codes, and emissions data.
• Drove 36 miles with no engine light but service DEF countdown continued.

Suggestions to Fix Issue:

• Replace both NOx sensors as they are often the issue with P2201.
• Check connections and circuits before buying new sensors.
• Consider testing the knock sensor for resistance or reaction to block knocks.
• Test and potentially replace the DEF fluid.
• Check for pending NOx system codes after a road test with no CEL.
• Ensure PCM completes a successful monitor test of the SCR catalyst.
• Address any vehicle modifications or usage of a programmer.
• Fulfill any open recalls, especially those related to the SCR Catalyst, and take an extended highway test drive to complete SCR monitor.

Final Fix:

• Replaced both NOx sensors and test drove over 50 miles without the check engine light returning.
• Discovered a recall (U84) issued for SCR catalyst replacement after extensive troubleshooting.
• Released the truck to the owner to have the recall service performed, pending confirmation on whether the recall resolved the issue.

Case #3: BMW

Vehicle Information:
2009 BMW X5 xDrive35d 3.0L, MIL Lamp on

Issue + Repair History:

• No start message in 180 miles due to the wrong DEF fluid added.
• Drained and refilled both DEF tanks with the correct BMW fluid.
• Unable to clear two codes: P2201 (NOx sensor performance) and P207F (incorrect DEF fluid).

Suggestions to Fix Issue:

• Check if the wrong fluid damaged any components and consider replacing them if necessary.
• Ensure tanks are completely filled, as it’s a requirement for the system to reset.
• Drive approximately 50 miles or more to see if the system resets on its own.
• Consider replacing both tanks and all SCR components if wrong fluid caused significant issues.
• Run a test plan for the NOx sensor and other related components like DOC cat or DME.
• Try cycling the key after filling the DEF: 3 times with a 30-second interval and once more leaving the key on for about 5 minutes before starting and driving the vehicle.

Final Fix:

• Sent the vehicle to the dealer for SCR adaptation reset and/or replacement of the NOx sensor.
• Noted for future instances to try driving for 50 miles or so to see if the system resets on its own.

Case #4: Mercedes

Vehicle Information:
2011 Mercedes-Benz Sprinter 3500 3.0L, MIL Lamp on

Issue + Repair History:

• Lacking bi-directional control and access to the DEF module for DEF codes with current tools.
• DEF was at 32.5% before a typo correction to 35.5%.
• Unable to perform tests for codes due to tool limitations.
• Released the vehicle to the customer, advised to visit the dealer for repair.

Suggestions to Fix Issue:

• Consider scan tools like Texa or Autologic for better diagnosis, particularly for SCR systems.
• The codes P2201, P20C0, and P20BC suggest issues with the NOx sensor and heating elements in the Adblue tank.
• For P2201 (upstream NOx sensor), check if the upstream NOx reading is higher than downstream as it should be.
• Consider draining and discarding the Adblue if the urea content is high (35.5%).
• If unable to afford the MB tool, consider aftermarket clones for guided diagnostics.
• Lower the DEF tank and check the harness for DEF crystallization; replace if found.
• Test the resistors for the heaters; they should be about 4 Ohms.
• Clear codes and attempt to force a regen, if possible.

Final Fix:

• Concluded that factory tooling is needed to work on these vans effectively; updates from Snap-on were insufficient.
• Started sending vehicles to the dealer if the issue is beyond the current capability.

Case #5: BMW

Vehicle Information:
2009 BMW X5 xDrive35d 3.0L, Excessive Emissions

Issue + Repair History:

• Vehicle showing problems with the urea system.
• Previous visit indicated a loose EGR cooler.

Suggestions to Fix Issue:

• Check the NOx sensor circuit using the wiring diagram; the sensor might be faulty.
• Contact the dealer to confirm if parts are under warranty as diesels can be complex.
• Check with BMW North America for possible coverage under emissions/powertrain warranty.
• Obtain detailed factory information, including repair instructions and diagrams, from www.bmwtechinfo.com using the vehicle’s VIN.
• Use a wiring schematic to diagnose the NOx sensor circuit code, which might be the primary issue.
• Be aware of common emission-related issues on similar BMW diesel models.

Final Fix:

• The problem was resolved by addressing a blown EGR cooler gasket that was allowing air into the exhaust stream, disrupting sensor readings.

Advice	Brief Description of Diagnostic Step
Check NOx sensor circuit	Use wiring diagrams to check for faults in the NOx sensor’s circuit.
Consider replacing NOx sensors	If diagnostics point to a faulty NOx sensor, consider replacing it.
Consult with the dealer	Confirm if the vehicle parts are still under warranty for free repair.
Obtain proper diagnostic tools	Use a capable scan tool for accurate diagnostics and bi-directional control.
Ensure correct DEF fluid	Check and ensure the DEF fluid is of the correct type and quality.
Inspect related components	Look at EGR coolers, heaters, and other associated components for faults.