How to Diagnose and Replace an EGR Delta Pressure Sensor on John Deere Tractors

Diagnosing and Replacing an EGR Delta Pressure Sensor on a John Deere 8235R

When engine fault codes appear on your tractor, narrowing down the issue quickly can save you time in the field and money in repairs. That’s exactly what we encountered on a service call on a John Deere 8235R showing EGR-related codes. Below is a breakdown of how we diagnosed the issue, tested the components, and confirmed the fix.

The Codes That Showed Up

Upon arrival, we connected the tractor to Service Advisor. Right away—engine off, key on—the system threw fault code 2659.04, a Delta Pressure Sensor Circuit fault code for the EGR system. We also saw another code, 1569.31, which was a derate code. The customer had originally reported fault code 2659.15, pointing to EGR Flow High.

Our focus turned to the delta pressure sensor to get to the root of the problem.

Running Diagnostics

To begin with, we used Service Advisor's harness diagnostics feature to check the whole system. This ran through all engine components, including the turbo actuator and sensors. After the scan, the two original codes were still active.

Testing the Sensor Circuit

Next, we physically inspected the delta pressure sensor. We confirmed the connector was seated properly and tested each pin for integrity. All connections checked out, so we moved on to verifying power, ground, and signal using the John Deere Engine Test Box.

Power and Ground: We hooked into the power and ground wires, and the meter was within spec, showing a solid 5 volts.

Load Test: We added a slight load to simulate real-world usage. The voltage dipped slightly but stayed within the acceptable range.

Wiggle Test: We moved around the harness to see if the voltage dropped—everything held steady.

Then we checked the signal wire, which read approximately 2.5 volts—within spec.

Wiring issues were ruled out with power, ground, and signal; all testing was good.

Installing a New Sensor

Though the wiring checked out, the sensor's voltage readings remained unstable. Even after shutting the tractor off, the Service Advisor still showed pressure readings—an obvious red flag.

We unbolted the pressure sensor, but it continued to show pressure when disconnected. That confirmed the sensor was faulty.

After plugging in a new, updated EGR Delta Pressure Sensor, the readings immediately corrected. We installed the new sensor, cleared the codes, and ran the tractor through a service regen. No new codes appeared, and the system operated as expected.

Final Results

After completing the regen, the tractor was returned to the customer and is now back in the field running normally. This service call is a good reminder of how important it is to verify sensor data and wiring before replacing parts. In this case, a simple sensor swap solved what could’ve become a bigger issue.