DDEC III/IV Single ECM Troubleshooting – Section 27.3 Troubleshooting Flash Code 27

Section 27.3
Troubleshooting Flash Code 27

The following procedure will troubleshoot Flash Code 27.‪

Section 27.3.1
Sensor Check

Perform the following steps to check the sensor.‪

1. Turn vehicle ignition OFF.
2. Disconnect ATS connector.
3. Install a jumper wire between sockets A and B of the ATS harness connector. See Figure "Air Temperature Sensor" .
4. Turn ignition ON.
5. Start and run engine for one minute; (ensure oil temp is greater than 140°F).
6. Read active codes.
   1. If code 172/4 or any other codes except 172/3 are logged, refer to "27.3.2 Check for Short to +5 Volt Line" .
   2. If any codes except code 172/4 are logged, refer to "27.3.4 Open Line Check" .
   

   Figure 1. Air Temperature Sensor

Section 27.3.2
Check for Short to +5 Volt Line

Perform the following steps to check for a short to the +5 volt line.‪

1. Turn ignition/engine OFF.
2. Remove jumper wire.
3. Disconnect the engine harness connector at the ECM.
4. Measure resistance between sockets N2 and W1 on the engine harness connector. See Figure "ECM Engine Harness Connector" .
   1. If the resistance measurement is less than or equal to 10 Ω, the signal line #132 is shorted to the engine +5 volt line (#416). Repair the short and refer to "27.3.6 Verify Repairs" .
   2. If the resistance measurement between sockets N2 and W1 is greater than 10 Ω or open, refer to "27.3.3 Check Air Temperature Sensor Connectors" .
   

   Figure 2. ECM Engine Harness Connector

Section 27.3.3
Check Air Temperature Sensor Connectors

Perform the following steps to check the ATS connectors.‪

1. Check terminals at the ATS connector (both sensor and harness side) for damage; bent, corroded and unseated pins or sockets. See Figure "Air Temperature Sensor" .
   1. If terminals or connectors are damaged, repair them. Refer to "27.3.6 Verify Repairs" .
   2. If terminals and connectors are not damaged, replace the ATS. Refer to "27.3.6 Verify Repairs" .
   

   Figure 3. Air Temperature Sensor

Section 27.3.4
Open Line Check

Perform the following steps to check for an open line.‪

1. Turn ignition OFF.
2. Disconnect the engine harness connector at the ECM. (Jumper still in place.)
3. Measure resistance between sockets N2 and Y2 on the engine harness connector. See Figure "ECM Engine Harness Connector" .
   1. If the resistance measurement is less than or equal to 5 Ω, refer to "27.3.5 Check ECM Connectors" .
   2. If the resistance measurement between sockets N2 and W1 is greater than 5 Ω or open, the signal line #132 or return line #452 is open. Repair the open. Refer to "27.3.6 Verify Repairs" .
   

   Figure 4. ECM Engine Harness Connector

Section 27.3.5
Check ECM Connectors

Perform the following steps to check the ECM connectors.‪

1. Check terminals at the ECM engine harness connector (both ECM and harness side) for damage: bent, corroded and unseated pins or sockets. See Figure "ECM Engine Harness Connector" .
   1. If terminals or connectors are damaged, repair them. Refer to "27.3.6 Verify Repairs" .
   2. If terminals and connectors are not damaged, contact Detroit Diesel Technical Service. Refer to "27.3.6 Verify Repairs" .
   

   Figure 5. ECM Engine Harness Connector

Section 27.3.6
Verify Repairs

Perform the following steps to verify repairs.‪

1. Turn vehicle ignition OFF.
2. Reconnect all connectors.
3. Turn vehicle ignition ON.
4. Clear codes.
5. Start and run the engine for eight minutes.
6. Stop engine.
7. Check DDR for codes.
   1. If no codes are logged, troubleshooting is complete.
   2. If code 172/3 and any other codes are logged, all system diagnostics are complete. Review this section to find the error. Refer to "27.3.1 Sensor Check" .
   3. If any codes except code 172/3 are logged, refer to "9.1 First Step for Diagnosing a Fault Within the DDEC System" .