Diagnostic Instructions
DTC Descriptors
DTC P1446: Pre-Catalyst Temperature Too Low During Regeneration
DTC P1447: Pre-Catalyst Temperature Too High During Regeneration
DTC P244C: Catalyst Temperature Too Low During Regeneration
Circuit/System Description
The diesel exhaust after-treatment system consists of an under hood pre-catalytic converter and an underbody catalytic converter. The underbody catalytic converter also consists of the main Diesel Oxidation Catalyst (DOC) and the coated Diesel
Particulate Filter (DPF). One of the main purposes of the DPF is to collect particulates from the engine exhaust in order to minimize discharge of soot to the atmosphere. The soot particles accumulate in the channels of the DPF and are burned off at regular
intervals through a process called regeneration. This prevents the DPF from clogging. The ECM commands the DPF regeneration after calculating various vehicle conditions such as DPF pressure difference, exhaust gas temperature, engine oil quality, engine speed,
etc. Excessive accumulation of the soot in the DPF can cause a drop in the engine performance. During regeneration, additional fuel is injected via multiple post injections in order to increase the exhaust gas temperature. During this period, the DPF temperature
is raised to approximately 600°C and the accumulated soot is oxidized or burned off into carbon dioxide (CO2).
Conditions for Running the DTC
The DTC runs during the DPF regeneration process.
Conditions for Setting the DTC
P1446
The actual temperature of the exhaust gas temperature (EGT) sensor 1 is 200°C (392°F) less than the desired temperature.
P1447
The actual temperature of the exhaust gas temperature (EGT) sensor 1 is 100°C (212°F) greater than the desired temperature.
P244C
The actual temperature of the exhaust gas temperature (EGT) sensor 2 is 125°C (257°F) less than the desired temperature.
Action Taken When the DTC Sets
DTCs P1446, P1447, and P244C are Type A DTCs.
Conditions for Clearing the DTC
DTCs P1446, P1447, and P244C are Type A DTCs.
Diagnostic Aids
| • | If the engine has sat overnight, both EGT sensors and the ECT sensor values should display within 3°C (5°F). |
| • | After starting a cold engine, the EGT sensors temperature should rise steadily, then stabilize. |
| • | High resistance in the circuits of either of the EGT sensors could set a DTC. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition On, observe the DTC information with a scan tool. Verify no other DTCs are set.
- Engine running, perform a regeneration procedure with a scan tool. Observe the DTC information with a scan tool. DTCs P1446, P1447, and P244C should not set.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the appropriate EGT sensor.
- Test for less than 5 ohms between the low reference circuit terminal 2 and ground.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
- Install the MAIN fuse. Ignition ON, verify the scan tool EGT sensor parameter is at 5 volts.
| ⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
Important: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.
- Install a 1A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool EGT sensor parameter is at 0 volts.
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
- Inspect for the following conditions:
| • | Intake and exhaust system for leaks or restrictions |
| • | Fuel system for leaks or restrictions |
| • | Excessive water in fuel |
| • | EGR for normal operation |
| • | An engine mechanical condition |
| ⇒ | If a condition is found, repair as necessary. |
- If all circuits test normal, test or replace the EGT sensor.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Repair Verification
Ignition ON, observe the scan tool DPF soot mass parameter. The parameter should be less than 24 grams.
