Cummins ISX12 CM2250 (2010-12) Fault Code: 3251 PID: SID 326 SPN: 475 FMI: 16 Aftertreatment Diesel oxidation Catalyst Intake Temperature- Data Valid But Above Normal Operating Range- Moderately Severe Level

Circuit Description
The aftertreatment temperature sensors are used by the engine control module (ECM) to monitor the engine exhaust temperatures in the aftertreatment system. The aftertreatment temperature sensors are thermistors and change resistance based on the temperature being measured. The ECM provides a 5 volt reference voltage to the sensor. The ECM monitors the change in signal voltage and converts this to a temperature value.

When the exhaust temperature is low, the sensor or thermistor resistance is high. The ECM signal voltage only pulls down a small amount through the sensor to ground. Therefore, the ECM senses a high signal voltage or a low temperature. When the exhaust gas temperature is high, the sensor resistance is low. The signal voltage pulls down a large amount. Therefore, the ECM senses a low signal voltage, or a high temperature.

Component Location
The aftertreatment DOC intake temperature sensor is located in the aftertreatment system, between the outlet of the turbocharger and intake of the exhaust aftertreatment. Refer to the original equipment manufacturer (OEM) service manual.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the engine is running and active regeneration of the aftertreatment DPF is not occurring.

Conditions for Setting the Fault Codes
The ECM detects that the temperature at the diesel oxidation catalyst intake is greater than 687?C [1269?F] for 60 seconds.

Action Taken When the Fault Code is Active
The ECM illuminates the red STOP ENGINE lamp immediately after the diagnostic runs and fails.
A default value for the aftertreatment DOC intake temperature sensor reading is used.
Active and stationary (parked) regeneration will be disabled.
Engine shutdown will occur 30 seconds after the fault becomes active. In all calibrations, except for emergency vehicle calibrations, engine shutdown will occur after 30 seconds, if engine protection shutdown is enabled or disabled. Engine shutdown will not occur in emergency vehicle calibrations.
Conditions for Clearing the Fault Code
To validate the repair using a Diagnostic Road Test, utilize a route that incorporates both stop-and-go city driving and steady state highway driving. It may be necessary to load the unit for certain diagnostics in the ECM to run.
To validate the repair using a Chassis Dynamometer Test, utilize a routine that incorporates acceleration and motoring events, steady state highway operation, and load. This will simulate normal driving and allow the diagnostics in the ECM to run.
The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the red STOP ENGINE lamp after the diagnostic runs and passes.
The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults.

Shop Talk
This fault code is logged when the ECM has detected a high temperature condition in the aftertreatment system and active regeneration of the aftertreatment DPF is not occurring. The fault code indicates that a secondary fuel source is entering the aftertreatment system and is creating a temperature increase across the aftertreatment DOC and/or aftertreatment DPF.

Possible causes of this fault code include:

Excessive engine oil or diesel fuel being introduced into the exhaust system from the engine
A damaged engine fuel injector causing unburned diesel fuel to enter the exhaust system
The aftertreatment DOC intake temperature sensor malfunctioned in-range
The aftertreatment DPF intake temperature sensor malfunctioned in-range
The aftertreatment DPF outlet temperature sensor malfunctioned in-range
An in-range engine sensor malfunction has occurred, causing excessive fuel to enter the exhaust system.
The aftertreatment system must be inspected after making the appropriate repair outlined in this fault code troubleshooting tree. Progressive damage to the aftertreatment system may have occurred. Remove the exhaust aftertreatment system from the vehicle to inspect it for potential damage and reuse. Refer to the original equipment manufacturer (OEM) service manual.

Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

For intermittent power supply and data link communication issues with aftertreatment components, it is highly recommended that the OEM power distribution center fuses and relays be thoroughly checked for loose, missing, or intermittent connections.

Possible Cause:
1) ECM calibration