Service Exhaust Fluid System: Troubleshooting GM trucks

Understanding the Service Exhaust Fluid System Message

A Service Exhaust Fluid System message is common on GM trucks. This message indicates a problem with the vehicle’s Exhaust Fluid System, which is crucial for meeting emissions standards. Understanding what this message means and how to address it can help ensure your truck remains in peak condition and compliant with environmental regulations.

GM has issued service bulletins #PIP4887A and #12-06-04-002E to address a Service Exhaust Fluid System Message and trouble codes P203D, P21AB, or P21B0 on the trucks listed below. If you see the “Service Exhaust Fluid System” and a “See Owner’s Manual Now” message displayed on the instrument cluster and scan the vehicle and find trouble codes P203D, P21AB, and P21B0, this bulletin may apply to you.

P203B  –  Reductant Level Sensor Performance: The ECM receives a serial data message from the reductant sensor module that the reductant level sensor indications are not plausible

P203C  –  Reductant Level Sensor 1 Circuit Low Voltage. The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is less than 0.17 V for greater than 3 s. A voltage within this range indicates a short to ground.

P203D  –  Reductant Level Sensor 1 Circuit High Voltage.  The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is between 3.56-4.74 V for greater than 3 s. A voltage within this range indicates an open circuit, or
The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is greater than 4.74 V for greater than 3 s. A voltage within this range indicates a short to voltage.

P21AA  –  Reductant Level Sensor 2 Circuit Low Voltage. The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is less than 0.17 V for greater than 3 s. A voltage within this range indicates a short to ground.

P21AB  –  Reductant Level Sensor 2 Circuit High Voltage. The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is between 3.56-4.74 V for greater than 3 s. A voltage within this range indicates an open circuit, or
The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is greater than 4.74 V for greater than 3 s. A voltage within this range indicates a short to voltage.

P21AF –  Reductant Level Sensor 3 Circuit Low Voltage. The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is less than 0.17 V for greater than 3 s. A voltage within this range indicates a short to ground.

P21B0  –  Reductant Level Sensor 3 Circuit High Voltage. The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is between 3.56-4.74 V for greater than 3 s. A voltage within this range indicates an open circuit, or
The ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2 or 3 voltage is greater than 4.74 V for greater than 3 s. A voltage within this range indicates a short to voltage.

Models Affected by PIP4887A

2010-2011 Chevrolet Express, Silverado
2010-2011 GMC Savana, Sierra
Equipped with 6.6L Duramax Diesel Engine RPO codes LML or LGH

What the Service Exhaust Fluid P203D P21AB or P21B0 means

The reductant tank has a level/temperature sensor inside that tells the ECM the reductant level and temperature. The level/temperature sensor gets power from the underhood electrical center and grounds through a chassis ground circuit.

The level sensor has three sensing elements. Reductant level sensor 3 is highest, reductant level sensor 2 is located between sensor 1 and 3. Reductant level sensor 1 is located at low reductant level. Reductant level sensor 3 is located at less than half range of the DEF tank level.

The reductant sensor module converts the analog data to a digital serial message to the ECM.

Diagnose Service Exhaust Fluid message

Using a digital meter, check the resistance of the

Reductant tank heater

reductant tank heater #1. Disconnect the Glow Plug Control Module and check the resistance reading on pin 11 (orange/white) and ground. You should see 2-4Ω. If the tank heater resistance is off, replace the heater. After replacing the heater, use a scan tool to perform a reductant fluid tank level reset. Then, perform a reductant system leak test. The system must hold 61-83-psi. Finally, use a scan tool to command each of the heaters on, one at a time, for at least 10 seconds each.

When diagnosing emission conditions, check for:
• Aftermarket air cleaners
• Diesel Airflow Leak Equivalency Ratio and DTC P0101
• Incorrect calibrations
• Exhaust leaks
• Charge air cooler system leaks
• DEF contamination.

©, 2020 Rick Muscoplat