TriPac APU 3rd generation Exhaust After Treatment Device (ATD) Codes / System Alarms

Additional ATD system alarm code information can be found in the TriPac 3 Diagnostic Manual TK 57116.

Code 367 – Check Exhaust Back-pressure Sensor
Note: The exhaust pressure sensor of previous generation TriPac units looks similar, but internally different and must
not be interchanged.
Alarm will self-clear when valid reading is present for greater than 10 seconds.
Condition 1 (Check Alarm): Open Circuit Detected - Open circuit detected for 2 consecutive seconds. Sets
sensor reading as invalid and will default to Time Based Regeneration.
Troubleshooting Steps:
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness.
• Check wires are not broken and verify the continuity in harness.
• Faulty Sensor, replace sensor and verify issue resolved.
Condition 2 (Check Alarm): Short Circuit Detected – Short circuit detected for 2 consecutive seconds. Sets
sensor reading as invalid and will default to Time Based Regeneration.
Troubleshooting Steps:
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness.
• Check wires are not broken or shorted and verify the continuity in harness.
• Faulty Sensor, replace sensor and verify issue resolved.
Condition 3 (Check Alarm): No pressure response – Exhaust pressure fails to increase 0.5 kPa from off state
when engine is running. Sets sensor reading as invalid and will default to Time Based Regeneration
Troubleshooting Steps:
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness.
• Check voltage supply to sensor is approximately 5 Vdc.
• Verify pressure tube to pressure sensor is not clogged. It can be removed and cleaned with non-oxygenated
automotive brake cleaner if clogged.
• Verify pressure tube fitting on exhaust vibrasorber is clean. Use a metal rod or brush to clean fitting orifice.
Condition 4 (Check Alarm): Excessively high pressure - If pressure is greater than 107 kPa when engine is off for
10 seconds. Sets sensor reading as invalid default to Time Based Regeneration
Troubleshooting Steps:
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness.
Note: The exhaust pressure sensor of previous generation TriPac units looks similar, but internally different and
must not be interchanged.
• Check voltage supply to sensor is approximately 5 Vdc.
• Verify pressure tube to pressure sensor is not clogged. It can be removed and cleaned with non-oxygenated
automotive brake cleaner if clogged.
• Verify pressure tube fitting on exhaust vibrasorber is clean. Use a metal rod or brush to clean fitting orifice.
• Verify air pump is not continuously running.
Condition 5 (Check Alarm): Low pressure - Exhaust pressure is less than 57 kPa when system is off. Sets sensor
reading as invalid and will default to Time Based Regeneration.
Troubleshooting Steps:
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness.
• Check voltage supply to sensor is approximately 5 Vdc.
• Verify pressure tube to pressure sensor is not clogged. It can be removed and cleaned with non-oxygenated
automotive brake cleaner if clogged.
• Verify pressure tube fitting on exhaust vibrasorber is clean. Use a metal rod or brush to clean fitting orifice.
• Altitude is greater than 16400 feet (5000 meters).

Exhaust Aftertreatment Device (ATD) System General Information (If Equipped)

Code 368 – ATD Regeneration Required
Condition 1 (Shutdown Alarm): Max runtime limit reached - Alarm will trigger if it has been over 130 engine
hours since the last regeneration.
Condition 2 (Shutdown Alarm): Max time based regeneration limit reached – When there is a pressure sensor
fault the system will revert to a time based regeneration instead of using the pressure sensor as control. Only 5
time based regenerations can be done before this alarm is triggered and the system needs to be fixed.
Condition 3 (Check Alarm): Condition 1 or 2 present and a manual regeneration requested.
Troubleshooting Steps:
• First, correct any pressure sensor alarms issues.
• Verify pressure tube to pressure sensor is not clogged. It can be removed and cleaned with non-oxygenated
automotive brake cleaner if clogged.
• Verify all systems are intact and not bypassed (i.e. ATD still present, pressure sensor installed, etc.).
• Verify that the ATD system is sealed properly and their are no exhaust leaks.
The alarm will self-clear after a successful standard regeneration.

Code 369 – ATD Regeneration Efficiency Low
Condition 1 (Check Alarm) – If 5 mandatory regenerations (20 kPa threshold reached) occur within a 10 engine
run hour period the alarm will set.
Troubleshooting Steps:
• Review system for other alarms and resolve them first.
• If system has significant hours on it, ash could have built up within the filter.
• Check engine history for any indication of high oil consumption.
• Verify the ATD absolute pressure sensor is installed and connected to the unit harness and working properly.
• Check for low current during regeneration. At 12 Vdc the ATD heater should draw 70A or higher.
• Verify air from the air pump is flowing to the ATD canister.
• Verify the pressure sensor tube and fitting are clean and free flowing.
• Verify the air pump tubing is sealed and not leaking.
• If the ATD filter is severely saturated, oxygen may not be able to get to the filter to allow oxidation of the particulate
matter. The back half of the filter can be removed from the housing and an open air regeneration can be attempted.

Code 370 – Regeneration Incomplete
Condition 1 (Log Alarm): Regeneration terminated early due to low battery voltage.
Condition 2 (Check Alarm): 2nd consecutive regeneration terminated due to low battery voltage (battery
voltage under 11.0 Vdc).
Alarm Code 371 – Check Heater
Condition 1 (Check Alarm): Open Circuit Detected - output will be de-energized.
Troubleshooting Steps:
• Check external connections: Ground (B-) connection on frame, and Positive (B+) connection at heater.
• Check 125A ATD fuse on positive cable.
• Verify wires are still connected on inside of heater.
Condition 2 (Check Alarm): Short Circuit Detected – output will be de-energized.
Troubleshooting Steps:
• Verify that the ATD heater wires are not broken or shorted. Check for rub points where the wired enter the ATD
canister and enter the APU unit back panel.
• Check for external damage on ATD housing. If the housing is dented it could be touching the internal filter element.
• Check for loose wires internally in the ATD housing.
• Check ATD heater resistance with a micro-ohm meter. The heater and wires should be between 0.14 and 0.16 ohms.
Exhaust Aftertreatment Device (ATD) System General Information (If Equipped)

Important: A standard ohm meter does not have the sensitivity to accurately measure ohms down to this range; amicro-ohm meter must be use to accurately measure the resistance of the heater.

Condition 3 (Check Alarm): Low Current during regeneration (Less than 50 amp current draw from heater) – No change in operation
Troubleshooting Steps:
• Heater should draw greater than 70 amps with 12 Vdc. Check for loose connections or abnormally high resistance in
the filter cartridge. Check ATD heater resistance with a micro-ohm meter. The heater and wires should be between
0.14 and 0.16 ohms.
Important: A standard ohm meter does not have the sensitivity to accurately measure ohms down to this range; a micro-ohm meter must be use to accurately measure the resistance of the heater.

• Disconnect ground and positive cable and power filter directly with 12 Vdc supply and measure current. If current is
still low, filter could be defective. Remove filter and check condition.
• Use ammeter to verify the current reading matches the Tripac current reading. If not, verify the Tripac current measurement device is functioning properly.
Condition 4 (Shutdown Alarm): Mandatory regeneration and condition 1, 2, or 3 are present.

Code 372 – Check Air Supply
Condition 1 (Check Alarm): Open circuit detected - Air supply is de-energized.
Troubleshooting Steps:
• Check external connections: Ground (B-) connection on frame, and Positive (B+) connection at heater.
• Verify that the ATD heater wires are not broken or shorted. Check for rub points where the wired enter the ATD canister and enter the APU unit back panel.
Condition 2 (Check Alarm): Short Circuit Detected - Air supply is de-energized.
Troubleshooting Steps:
• Check wires at air pump for rubbing or degraded insulation.
• Verify that the ATD heater wires are not broken or shorted. Check for rub points where the wired enter the ATD
canister and enter the APU unit back panel.
• Check continuity of ATD system harnesses. Reference harness diagram for pinouts.

Code 375 – ATD Regeneration Not Allowed
Condition 1 (Check Alarm): Battery Voltage > 15 Vdc.
Troubleshooting Steps:
• Diagnose unit and truck charging system.
Condition 2 (Check Alarm): Battery Voltage Rises above 15 Vdc During Active Regeneration.
Troubleshooting Steps:
• Diagnose unit and truck charging system.
Condition 3 (Check Alarm): Service Switch is OFF
Troubleshooting Steps:
• Verify the service switch is in the ON position.