DDEC III/IV Single ECM Troubleshooting – Section 10.6 Diagnostic Request Switch Inoperative

Section 10.6
Diagnostic Request Switch Inoperative

Before using this procedure, all basic mechanical checks and physical inspections should have been performed with no problem found. Also the diagnosis of the DDEC system in Section 9 referred you to this section.‪

Section 10.6.1
Check Diagnostic Request Circuit

Perform the following steps to check the diagnostic request circuit:‪

1. Turn ignition ON; engine not running.
2. Plug in DDR.
3. Select Switch/Light Status.
4. Depress and hold diagnostic request switch.
5. Observe the Diagnostic Request Status on the DDR.
   1. If the display reads ON, refer to "10.6.2 Check Stop Engine Light and Check Engine Light Bulbs" .
   2. If the display reads OFF, the diagnostic request line (#528) is open, or is not being grounded when the switch is depressed. Check the #528 wire and ground for diagnostic request switch. Repair the problem; refer to "10.6.4 Verify Repairs" .
   3. If no diagnostic request on the DDR input list, the ECM is not configured for diagnostic request operation. Refer to the DDEC Application and Installation manual, 7SA800.

Section 10.6.2
Check Stop Engine Light and Check Engine Light Bulbs

Perform the following steps to check the SEL and CEL bulbs:‪

1. Turn ignition OFF.
2. Remove CEL and SEL bulbs. Check to see if either is burned out or damaged.
   1. If the bulbs are okay, refer to "10.6.3 Check 12V / 24V Ignition Line" .
   2. If the bulbs are defective, replace the bulbs. Refer to "10.6.4 Verify Repairs" .

Section 10.6.3
Check 12V / 24V Ignition Line

Perform the following steps to check the 12V/24V ignition line:‪

1. Turn ignition ON.
2. Disconnect vehicle harness connector at ECM.
3. Measure voltage at cavity B3 (#439).
   1. If voltage measurement is less than 11.5V, the 5–amp fuse or circuit breaker is blown, and the ignition line could be open or shorted to ground.
   2. If the voltage measurement is greater than 11.5V, the circuit #419 or #509 is open. Repair the open circuit. Refer to "10.6.4 Verify Repairs" .

Section 10.6.4
Verify Repairs

Perform the following steps to verify repairs:‪

1. Reconnect all connectors.
2. Turn ignition ON.
3. Press diagnostic request switch.
   1. If codes flash, the system is working. Repairs are complete. If any other problems exist, refer to "9.1 First Step for Diagnosing a Fault Within the DDEC System" .
   2. If the system does not function, all system diagnostics are complete. Review this section to find the error. Refer to "10.6.1 Check Diagnostic Request Circuit" .