Pinpoint Test H: The Scan Tool Indicates Self-Test Failure When Attempting to Carry Out the Self-Test

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Vehicle Dynamic Suspension for schematic and connector information.

Normal Operation 

In the ON position, a signal is sent from the vehicle dynamics module (VDM) along circuit 417 (VT/OG) to the VDM along circuit 635 (YE) through the closed air suspension switch. The VDM receives this signal and activates the air suspension system. In the OFF position, this signal is interrupted by the open air suspension switch and the VDM deactivates the air suspension system.

• DTC C1840 Air Suspension Disable Switch Circuit Failure - If during the VDM on-demand self test, the air suspension switch is not in the ON position or the VDM detects an open, a short to voltage or a short to ground on the air suspension switch circuit, DTC C1840 will set.

This pinpoint test is intended to diagnose the following:

• Wiring, terminals or connectors
• Air suspension switch
• VDM

PINPOINT TEST H: DTC C1840 - THE SCAN TOOL INDICATES SELF-TEST FAILURE WHEN ATTEMPTING TO CARRY OUT THE SELF-TEST 

1. H1 CHECK THE AIR SUSPENSION SWITCH VOLTAGE 
   • Key in OFF position.
   • Disconnect: Air Suspension Switch C4087
   • Key in ON position.
   Fig 1: Checking Circuits For Voltage
   Courtesy of FORD MOTOR CO.
   • Measure the voltage between air suspension switch C4087-2, circuit 417 (VT/OG), harness side and ground.
   • Is the voltage approximately 5 volts? 
   1. YES  : Go to  H2.
   2. NO  : Go to  H4.
2. H2 CHECK CIRCUIT 635 (YE) FOR AN OPEN 
   • Disconnect: VDM C2131a
   • Disconnect: VDM C2131b
   Fig 2: Checking Circuit For Open
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between air suspension switch C4087-1, circuit 635 (YE), harness side and VDM C2131b-7, circuit 635 (YE), harness side.
   • Is the resistance less than 5 ohms? 
   1. YES  : Go to  H3.
   2. NO  : REPAIR circuit 635 (YE). CLEAR the DTCs. REPEAT the self-test.
3. H3 CHECK CIRCUIT 635 (YE) FOR A SHORT TO GROUND 
   Fig 3: Checking Circuit For Short To Ground
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between VDM C2131b-7, circuit 635 (YE), harness side and ground.
   • Is the resistance greater than 10,000 ohms? 
   1. YES  : Go to  H6.
   2. NO  : REPAIR circuit 635 (YE). CLEAR the DTCs. REPEAT the self-test.
4. H4 CHECK CIRCUIT 417 (VT/OG) FOR AN OPEN 
   Fig 4: Checking Circuit For Open
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between air suspension switch C4087-2, circuit 417 (VT/OG), harness side and VDM C2131b-4, circuit 417 (VT/OG).
   • Is the resistance less than 5 ohms? 
   1. YES  : Go to  H5.
   2. NO  : REPAIR circuit 417 (VT/OG). CLEAR the DTCs. REPEAT the self-test.
5. H5 CHECK CIRCUIT 417 (VT/OG) FOR A SHORT TO GROUND 
   Fig 5: Checking Circuit For Short To Ground
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between VDM C2131b-4, circuit 417 (VT/OG), harness side and ground.
   • Is the resistance greater than 10,000 ohms? 
   1. YES  : Go to  H6.
   2. NO  : REPAIR circuit 417 (VT/YE). CLEAR the DTCs. REPEAT the self-test.
6. H6 CHECK THE AIR SUSPENSION SWITCH 
   • Push the air suspension switch to the ON position.
   • Measure the resistance between air suspension switch pin 1, component side and pin 2, component side.
   • Is the resistance less than 5 ohms? 
   1. YES  : Go to  H7.
   2. NO  : INSTALL a new air suspension switch. REFER to Air Suspension Switch . CLEAR the DTCs. REPEAT the self-test.
7. H7 VERIFY VDM CONNECTIONS 
   • Check VDM connectors C2131a and C2131b for damage or loose connections.
   • Are the module connections OK? 
   1. YES  : INSTALL a new VDM. REFER to Vehicle Dynamics Module (VDM) .
   2. NO  : REPAIR the VDM connectors. CLEAR the DTCs. REPEAT the self-test.