DDEC III/IV Single ECM Troubleshooting – Section 12.3 Troubleshooting Flash Code 12

Section 12.3
Troubleshooting Flash Code 12

The following procedure will troubleshoot Flash Code 12.‪

Section 12.3.1
Multiple Code Check

Perform the following steps to check for multiple codes:‪

1. Turn ignition ON. (For VSG circuit, see Figure "Variable Speed Governor Circuit" .)
2. Plug in DDR.
   1. If active code 187/3 and any other codes except 91/3 or 100/3 are logged, refer to "12.3.2 Sensor Check" .
   2. If active code 187/3 and codes 91/3 or 100/3 are logged, refer to "91.2 Troubleshooting Vehicle Harness +5 Volt Supply" .
   

   Figure 1. Variable Speed Governor Circuit

Section 12.3.2
Sensor Check

Perform the following steps to check the sensor:‪

1. Turn ignition OFF.
2. Unplug the VSG throttle connector. (For VSG circuit, see Figure .)
3. Turn ignition ON.
4. Read active codes.
   1. If active code 187/4 is logged, and code 187/3 only occurs when the throttle is moved at or near full throttle (when connected), refer to "12.3.3 Check Calibration" .
   2. If active code 187/3 is logged, and the code appears when the throttle is not at or near full throttle (when connected), refer to "12.3.4 Return Circuit Check" .

Section 12.3.3
Check Calibration

Perform these additional steps to check the calibration of the sensor:‪

1. Plug in the VSG throttle connector.
2. Turn ignition ON.
3. Plug in DDR.
4. Display VSG counts.
5. Dial throttle to Full Throttle.
   1. If the VSG counts are greater than 968, adjust the maximum throttle travel. If not adjustable, replace the throttle control.
   2. If the VSG counts are less than 968, refer to "12.3.4 Return Circuit Check" .

Section 12.3.4
Return Circuit Check

Perform these steps to check the return circuit:‪

1. Place the transmission in neutral.
2. Turn ignition OFF.
3. Install a jumper wire between pin A (return #952) and pin B (signal #510/525) of the VSG throttle harness connector.
4. Disconnect the vehicle harness connector at the ECM.
5. Enable VSG control. (This may require the ignition be turned on.)
6. Measure resistance between sockets C3 (#952) and D1 (#510) on the vehicle harness connector. See Figure "Typical Variable Speed Governor Circuit" .
   1. If the resistance is less than or equal to 5 Ω, refer to "12.3.5 Variable Speed Governor Throttle Connector Check" .
   2. If the resistance is greater than 5 Ω , the return line (#952) is open, repair the open. Refer to "12.3.8 Verify Repairs" .
   

   Figure 2. Typical Variable Speed Governor Circuit

Section 12.3.5
Variable Speed Governor Throttle Connector Check

Perform these steps to check the VSG throttle connectors:‪

1. Inspect terminals at the VSG connectors (sensor side and harness side) for bent, corroded and unseated pins or sockets.
   1. If the VSG connector terminals are damaged, repair terminals and/or connectors. Refer to "12.3.8 Verify Repairs" .
   2. If the VSG connector terminals are in good condition with no signs of damage, refer to "12.3.6 Check for Short to Battery (+)" .

Section 12.3.6
Check for Short to Battery (+)

Perform these steps to check for short to battery (+).‪

1. Turn ignition OFF.
2. Unplug VSG connector.
3. Turn ignition ON.
4. Measure voltage between B (signal #525/#510) and battery ground. See Figure "Variable Speed Governor Circuit" .
   1. If measured voltage is less than or equal to 0.2 volts, refer to "12.3.7 Check for Short" .
   2. If measured voltage is greater than 0.2 volts, signal wire is shorted to 12/24 volt source. Repair or replace #510/#525 circuit. Refer to "12.3.8 Verify Repairs" .
   

   Figure 3. Variable Speed Governor Circuit

Section 12.3.7
Check for Short

To check for short, perform the following:‪

1. Turn ignition OFF.
2. Unplug vehicle 30-pin connector and the VSG connector.
3. Turn ignition ON.
4. Enable VSG. Refer to OEM guidelines.
5. Measure resistance between A3 (#916) and D1 (#510). See Figure "Variable Speed Governor Circuit" .
   1. If resistance is greater than 5 Ω, check ECM connector. Refer to "12.3.8 Verify Repairs" .
   2. If resistance is less than 5 Ω, wire #916 (5-volt supply) is shorted to #510/#525 (signal). Repair short or replace wire. Refer to "12.3.8 Verify Repairs" to verify repairs.
   

   Figure 4. Variable Speed Governor Circuit

Section 12.3.8
Verify Repairs

Perform the following steps to verify repairs.‪

1. Turn ignition OFF.
2. Reconnect all connectors.
3. Set parking brake, transmission in Neutral.
4. Turn ignition ON.
5. Clear codes.
6. Start and run the engine for one minute.
7. Stop engine.
8. Check DDR for codes.
   1. If no codes are displayed, no further troubleshooting is required.
   2. If code 187/3 is not logged, and other codes are logged, refer to "9.1 First Step for Diagnosing a Fault Within the DDEC System" .
   3. If code 187/3 is logged, and other codes are logged, refer to "12.3.1 Multiple Code Check" .