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Detroit Fault Codes SPN 51/FMI 18 – GHG14

25/11/2025
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SPN 51/FMI 18 - GHG14
Intake Throttle Position Rationality Error
SPN 51/FMI 18
Description This Fault Sets When Intake Throttle Position Does Not Match Requested Range
Monitored Parameter Intake Throttle Valve (ITV)
Typical Enabling Conditions Engine rpm = idle or higher
Monitor Sequence None
Execution Frequency Continuous when enabling conditions met
Typical Duration Five seconds
Dash Lamps MIL
Engine Reaction No Derate
Verification Engine rpm = idle or higher

Possible causes:

  • Damaged ITV butterfly flap
  • Faulty ITV motor
  • Faulty ITV sensor

Check as follows:

1. Check the Motor Control Module (MCM) software level. Compare the current MCM software level to the server. Is the MCM software at the latest level?

1.1. Yes; Go to step 2.

1.2. No; update the MCM software level and verify repair. If the fault code does not return, release the vehicle. If the fault code returns, Go to step 2.

2. Remove the hose from the Charge Air Cooler (CAC) to the ITV.

3. Visually inspect the ITV butterfly valve. Is there damage to the butterfly valve?

3.1. Yes; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

3.2. No; Go to step 4.

4. Connect Diagnostic Link™.

5. Turn the ignition ON (key ON, engine OFF).

6. Use the Service Routines greater than Intake Throttle Valve in DiagnosticLink to command the ITV fully open and fully closed while watching the ITV flap. Does the ITV butterfly valve fully close and fully open when commanded?

6.1. Yes; Go to step 7.

6.2. No; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

7. Using the Intake Throttle Valve service routine, command the ITV to 20% while monitoring the ITV actual position. Is the actual valve position within +/- 5% of the commanded position?

7.1. Yes; Go to step 8.

7.2. No; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

8. Command the ITV to 50% while monitoring the ITV actual position. Is the actual valve position within +/- 5% of the commanded position?

8.1. Yes; Go to step 9.

8.2. No; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

9. Command the ITV to 90% while monitoring the ITV actual position. Is the actual valve position within +/- 5% of the commanded position?

9.1. Yes; Go to step 10.

9.2. No; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

10. Turn the ignition OFF. Go to step 11.

11. Disconnect and inspect the ITV 5-pin connector. Are there any damaged pins, spread pins or the retainer clip missing?

11.1. Yes; repair as necessary. Verify repair.

11.2. No; Go to step 12.

12. Measure the resistance across pins 4 and 5, component side, of the ITV motor connector. Is the resistance less than 10 ohms?

12.1. Yes; Go to step 13.

12.2. No; replace the ITV due to a shorted motor. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

13. Install a test Motor Control Module (MCM). Go to step 14.

14. Road test the vehicle. Is code SPN 51/FMI 18 still present?

14.1. Yes; replace the ITV. Refer to section “Removal of the Intake Throttle Valve and Adaptor” . Verify repair.

14.2. No; replace the MCM. Refer to section “Removal of the Motor Control Module” . Verify repair.

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