For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P1446: Pre-Catalyst Temperature Too Low During Regeneration
DTC P1447: Pre-Catalyst Temperature Too High 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.

### Action Taken When the DTC Sets

DTCs P1446 and P1447 are Type A DTCs.

### Conditions for Clearing the DTC

DTCs P1446 and P1447 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

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition On, observe the DTC information with a scan tool. Verify no other DTCs are set.

⇒ | If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. Engine running, perform a regeneration procedure with a scan tool. Observe the DTC information with a scan tool. DTCs P1446 or P1447 should not set.
3. 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

1. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the appropriate B131 EGT sensor.
2. Test for less than 5 Ω 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 K20 ECM.

3. Install the MAIN fuse. Ignition ON, verify the scan tool exhaust gas temperature sensor parameter is at 5 V.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.

Note: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

4. Install a 1 A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool exhaust gas temperature sensor parameter is at 0 V.

⇒ | 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 K20 ECM.

5. 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

• | Plugged fuel filter

• | Restricted air filter

• | Turbocharger operation

• | An engine mechanical condition

⇒ | If a condition is found, repair as necessary.

6. If all circuits test normal, test or replace the B131 EGT sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Exhaust Temperature Sensor Replacement - Position 1.

• | Exhaust Temperature Sensor Replacement - Position 2.

• | Control Module References for ECM replacement, programming and setup

### Repair Verification

Ignition ON, observe the scan tool DPF accumulated soot mass parameter. The parameter should be less than 10 grams.

⇒ | If greater than the specified range, perform a DPF service regeneration. Refer to Exhaust Particulate Filter Cleaning.