P1484

P1484-CATALYST OVERHEAT DETECTION





For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

The Aftertreatment Diesel Oxidation Catalyst is designed to react with hydrocarbons in the exhaust stream, this reaction produces heat. The heat can become excessive if too much hydrocarbon enters the Aftertreatment Diesel Oxidation Catalyst too quickly. Excessive heat can damage the diesel aftertreatment components, so the temperature of the aftertreatment system is closely monitored by the ECM. The Exhaust Temperature Sensors are used by the ECM to monitor the temperatures throughout the aftertreatment system. The Exhaust Temperature Sensors are thermistors and change resistance based on the temperature being measured. The ECM provides a calibratable reference voltage to the sensor. The ECM monitors the voltage on the signal pin and converts this to a temperature value. When the exhaust gas temperature is cold, 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 low temperature. When the exhaust gas temperature is hot, 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. The ECM will illuminate the MIL lamp immediately when the diagnostic runs and fails. The ECM will also disable active regeneration of the aftertreatment diesel particulate filter. This DTC will not self clear and must be cleared by a scan tool.

- When Monitored:

Ignition ON.

- Set Condition:

The ECM detects that the Exhaust Temperature Sensor 1/1 temperature is greater than calibratable temperature for longer than a calibratable time.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.


1. TEMPERATURE SENSOR(S)

Turn ignition switch off.

Disconnect all three Exhaust Temperature Sensor harness connectors.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between the Signal circuits and the (K900) Sensor ground circuit of the each Exhaust Temperature Sensor.

Is the measured resistance between 82k and 300k ohms at ambient temperature?

Yes

- Go To 2

No

- Replace the out of range Exhaust Temperature Sensor.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. VOLTAGE HIGH

Ignition on, engine running.


NOTE: Vehicle coolant must be at a minimum of 120 degrees coolant temperature for a minimum of 5 minutes.

Using a scan tool, monitor the Exhaust Temperature Sensor Signal voltage of all three sensors.

Is the Exhaust Temperature Sensor signal voltage 4.75 VDC or greater for any of the temp sensors?

Yes

- Go To 4

No

- Go To 3

3. ECM

Turn ignition switch off.

Disconnect the engine wiring harness 12 way harness connector from the aftertreatment wiring harness 12 way harness connector.

Ignition on, engine not running.

Using a scan tool, monitor the EGR Temperature Sensor Signal voltage.

Is the EGR temperature sensor signal voltage 4.75 VDC or greater?

Yes

- Repair or replace engine harness
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Replace the ECM
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. OPEN HARNESS

Turn ignition switch off.

Disconnect the ECM harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Reconnect the ECM harness connector.

Turn the ignition switch on.

Using the scan tool, monitor the Exhaust Temperature Sensor Signal voltage

Is the temperature sensor signal voltage 4.75 VDC or greater?

Yes

- Repair or replace engine harness
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Replace The ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test