C175 Tier 4 Final Engines for Off-Highway Trucks Caterpillar

Backflow Valve - Test

Usage:

793F D3T

Use this procedure to troubleshoot a problem with a backflow valve. Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

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Table 1
J1939 Code and Description	CDL Code and Description	Comments
7598-5 Aftertreatment #1 DEF Backflow Valve #1 : Current Below Normal	5024-5 Aftertreatment #1 DEF Backflow Valve #1 : Current Below Normal	This code indicates that there is a problem with the aftertreatment #1 DEF backflow valve #1 and/or the electrical circuit for the backflow valve.
7598-6 Aftertreatment #1 DEF Backflow Valve #1 : Current Above Normal	5024-6 Aftertreatment #1 DEF Backflow Valve #1 : Current Above Normal	This code indicates that there is a problem with the aftertreatment #1 DEF backflow valve #1 and/or the electrical circuit for the backflow valve.
7599-5 Aftertreatment #1 DEF Backflow Valve #2 : Current Below Normal	5025-5 Aftertreatment #1 DEF Backflow Valve #2 : Current Below Normal	This code indicates that there is a problem with the aftertreatment #1 DEF backflow valve #2 and/or the electrical circuit for the backflow valve.
7599-6 Aftertreatment #1 DEF Backflow Valve #2 : Current Above Normal	5025-6 Aftertreatment #1 DEF Backflow Valve #2 : Current Above Normal	This code indicates that there is a problem with the aftertreatment #1 DEF backflow valve #2 and/or the electrical circuit for the backflow valve.
7600-5 Aftertreatment #2 DEF Backflow Valve #1 : Current Below Normal	5026-5 Aftertreatment #2 DEF Backflow Valve #1 : Current Below Normal	This code indicates that there is a problem with the aftertreatment #2 DEF backflow valve #1 and/or the electrical circuit for the backflow valve.
7600-6 Aftertreatment #2 DEF Backflow Valve #1 : Current Above Normal	5026-6 Aftertreatment #2 DEF Backflow Valve #1 : Current Above Normal	This code indicates that there is a problem with the aftertreatment #2 DEF backflow valve #1 and/or the electrical circuit for the backflow valve.
7601-5 Aftertreatment #2 DEF Backflow Valve #2 : Current Below Normal	5027-5 Aftertreatment #2 DEF Backflow Valve #2 : Current Below Normal	This code indicates that there is a problem with the aftertreatment #2 DEF backflow valve #2 and/or the electrical circuit for the backflow valve.
7601-6 Aftertreatment #2 DEF Backflow Valve #2 : Current Above Normal	5027-6 Aftertreatment #2 DEF Backflow Valve #2 : Current Above Normal	This code indicates that there is a problem with the aftertreatment #2 DEF backflow valve #2 and/or the electrical circuit for the backflow valve.

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Table 2
Required Tools		Qty
372-5260	Test Lead Tool Group	1

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Illustration 1	g06100050
The DEF pumps are on the front side of the Pump Electronic Tank Unit (PETU). (1) Aftertreatment #1 DEF Pump #1 (2) Aftertreatment #1 DEF Pump #2 (3) Aftertreatment #2 DEF Pump #1 (4) Aftertreatment #2 DEF Pump #2 (5) Coolant diverter valve for Aftertreatment #1 DEF Pump #1 (6) Coolant diverter valve for Aftertreatment #1 DEF Pump #2 (7) Coolant diverter valve for Aftertreatment #2 DEF Pump #1 (8) Coolant diverter valve for Aftertreatment #2 DEF Pump #2 (9) Aftertreatment #1 DEF Pump #1 header (10) Aftertreatment #1 DEF Pump #2 header (11) Aftertreatment #2 DEF Pump #1 header (12) Aftertreatment #2 DEF Pump #2 header (13) Aftertreatment #1 DEF Pump #1 backflow valve (14) Aftertreatment #1 DEF Pump #2 backflow valve (15) Aftertreatment #2 DEF Pump #1 backflow valve (16) Aftertreatment #2 DEF Pump #2 backflow valve (17) Aftertreatment #1 DEF Pump #1 electrical connection for DEF header (18) Aftertreatment #1 DEF Pump #2 electrical connection for DEF header (19) Aftertreatment #2 DEF Pump #1 electrical connection for DEF header (20) Aftertreatment #2 DEF Pump #2 electrical connection for DEF header

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Illustration 2	g06140989
The DEF injectors are on the inlet of the Clean Emissions Module (CEM). There are injectors on both inlets of the dual CEM applications. (21) DEF injector 2 (Aftertreatment 1 DEF pump 1) (22) DEF injector 3 (Aftertreatment 1 DEF pump 1) (23) DEF injector 1 (Aftertreatment 1 DEF pump 2) (24) DEF injector 4 (Aftertreatment 1 DEF pump 2) (25) DEF injector 2 (Aftertreatment 2 DEF pump 1) (26) DEF injector 3 (Aftertreatment 2 DEF pump 1) (27) DEF injector 1 (Aftertreatment 2 DEF pump 2) (28) DEF injector 4 (Aftertreatment 2 DEF pump 2)

Reference: Refer to Troubleshooting, System Overview (Aftertreatment Identification) for locating aftertreatment components if necessary.

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Table 3
Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Connect Cat^® Electronic Technician (ET) to the service tool connector. B. Determine if a code is active or logged.	Codes	Result: A -5 code is active or logged. Proceed to Test Step 2. Result: A -6 code is active or logged. Proceed to Test Step 3.
2. Check the Backflow Valve Wiring Harness for an Open Circuit A. Turn the keyswitch to the OFF position. The keyswitch must be OFF for 2 minutes to allow the DEF pump to purge, reset the code, and reset the Diesel Exhaust Fluid Controllers (DCU’s). B. Disconnect the Pump Electronic Tank Unit (PETU) wiring harness from the affected DEF backflow valve and the affected DCU. C. Connect the 398-5063 Probe to the DCU connector. The probe must be used to prevent damage to the DCU connector. D. Measure the resistance between the following terminals on the affected DEF backflow valve wiring harness connector and the affected 86-pin DCU wiring harness connector: - For Aftertreatment #1 DCU #1, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and Terminal 11 (DEF Backflow Valve (+)) on the 86-pin DCU connector. - For Aftertreatment #1 DCU #1, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and Terminal 31 (DEF Backflow Valve (-)) on the 86-pin DCU connector. - For Aftertreatment #1 DCU #2, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and Terminal 11 (DEF Backflow Valve (+)) on the 86-pin DCU connector. - For Aftertreatment #1 DCU #2, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and Terminal 31 (DEF Backflow Valve (-)) on the 86-pin DCU connector. - For Aftertreatment #2 DCU #1, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and Terminal 11 (DEF Backflow Valve (+)) on the 86-pin DCU connector. - For Aftertreatment #2 DCU #1, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and Terminal 31 (DEF Backflow Valve (-)) on the 86-pin DCU connector. - For Aftertreatment #2 DCU #2, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and Terminal 11 (DEF Backflow Valve (+)) on the 86-pin DCU connector. - For Aftertreatment #2 DCU #2, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and Terminal 31 (DEF Backflow Valve (-)) on the 86-pin DCU connector.	Open Circuit	Result: There were less than 10 Ohms of resistance on all the circuit wires between the affected backflow valve and the affected DCU. Proceed to Test Step 3. Result: There were more than 10 Ohms of resistance on all the circuit wires between the affected backflow valve and the affected DCU. Repair: An open circuit has been detected. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Proceed to Test Step 5.
3. Check the Backflow Valve Wiring Harness for a Short Circuit A. Turn the keyswitch to the OFF position. The keyswitch must be OFF for 2 minutes to allow the DEF pump to purge, reset the code, and reset the DCU’s. B. Disconnect the PETU wiring harness from the affected DEF backflow valve and the affected DCU. C. Connect the 398-5063 Probe to the DCU connector. The probe must be used to prevent damage to the DCU connector. D. Measure the resistance between the following terminals on the affected DEF backflow valve wiring harness connector and a known good chassis ground: - For Aftertreatment #1 DCU #1, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #1 DCU #1, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #1 DCU #2, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #1 DCU #2, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #2 DCU #1, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #2 DCU #1, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #2 DCU #2, Terminal 1 (Supply) on the affected DEF backflow valve wiring harness connector and a known good ground. - For Aftertreatment #2 DCU #2, Terminal 2 (Return) on the affected DEF backflow valve wiring harness connector and a known good ground.	Short Circuit	Result: There were more than 100K Ohms of resistance on all the circuit wires between the affected backflow valve and a known good ground. Proceed to Test Step 4. Result: There were less than 100K Ohms of resistance on all the circuit wires between the affected backflow valve and a known good ground. Repair: A short circuit has been detected. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Proceed to Test Step 5.
4. Check the DCU Wiring Harness Connector for a Short Circuit A. Turn the keyswitch to the OFF position. The keyswitch must be OFF for 2 minutes to allow the DEF pump to purge, reset the code, and reset the DCU’s. B. Disconnect the PETU wiring harness from the affected DEF backflow valve and the affected DCU. C. Connect the 398-5096 Probe to the DCU connector. The probes must be used to prevent damage to the DCU connector. D. Measure the resistance between the following terminals in the affected 86-pin DCU wiring harness connector: - For Aftertreatment #1 DCU #1, Terminal 11 (Supply) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #1 DCU #1, Terminal 2 (Return) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #1 DCU #2, Terminal 1 (Supply) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #1 DCU #2, Terminal 2 (Return) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #2 DCU #1, Terminal 11 (Supply) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #2 DCU #1, Terminal 2 (Return) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #2 DCU #2, Terminal 1 (Supply) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector. - For Aftertreatment #2 DCU #2, Terminal 2 (Return) on the affected DCU 86-pin wiring harness connector and all other pins in the 86-pin connector.	Short Circuit	Result: There were more than 100K Ohms of resistance on all the wires between the affected DCU wiring harness connector and all other pins in the affected DCU wiring harness connector. Repair: Replace the affected backflow valve. Proceed to Test Step 5. Result: There were less than 100K Ohms of resistance on all the wires between the affected DCU wiring harness connector and all other pins in the affected DCU wiring harness connector. Repair: A short circuit has been detected. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Proceed to Test Step 5.

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Illustration 3	g06026979

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Table 4
5. Perform the "Aftertreatment Dosing System Functional Test". A. Turn the keyswitch to the ON position. Do not start the engine. B. Connect Cat ET. C. Select the "Selective Catalyst Reduction System". D. Perform the following diagnostic test: -"Aftertreatment Dosing System Functional Test" Refer to Troubleshooting, Cat ET Service Features for additional information. Note: When the test prompts to proceed to clear active diagnostics, select ACCEPT.	Test	Result: The test was successful. Return to service.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).