LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2005 >> XLR >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls (DTC P0638 To P2095) >> DTC P0687 >> Test Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test Description

  1. 2:  The engine will crank but will not run with a short to battery positive voltage, or a short to the ignition 1 voltage on the ignition 1 relay coil control circuit.
DTC P0687

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2 
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition, with the engine OFF.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze/Frame Failure Records.
Did the DTC fail this ignition?		 - Go to Step 3  Go to Intermittent Conditions
3
  1. Turn OFF the ignition.
  2. Remove the ignition 1 relay from the underhood fuse block with the J 43244  Relay Puller Pliers. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) in Wiring Systems.
    3. NOTE: Refer to Test Probe Notice in Cautions and Notices.
  3. Probe the ignition 1 relay coil control circuit terminal at the underhood fuse block, with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate?		 - Go to Step 7  Go to Step 4 
4
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition 1 relay coil control circuit terminal at the underhood fuse block with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 5  Go to Step 9 
5
  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) electrical connector that contains the ignition 1 relay coil control circuit. Refer to Engine Control Module (ECM) Replacement . Turn ON the ignition, with the engine OFF.
  3. Turn ON the ignition, with the engine OFF.
    4. NOTE: Refer to Test Probe Notice in Cautions and Notices.
  4. Probe the ignition 1 relay coil control circuit at the underhood fuse block with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 6  Go to Step 13 
6
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical.
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 relay coil control circuit. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.
  4. Disconnect the ignition 1 relay coil control circuit terminal from the underhood fuse block electrical connector. Refer to Push to Seat Connectors in Wiring Systems.
  5. Connect the electrical connector that contained the ignition 1 relay coil control circuit to the underhood fuse block.
  6. Connect the negative battery cable at the battery.
  7. Turn ON the ignition, with the engine OFF.
  8. Probe the ignition 1 relay coil control circuit terminal at the electrical connector for the underhood fuse block with a test lamp that is connected to good ground.
Does the test lamp illuminate?		 - Go to Step 14  Go to Step 17 
7
  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) electrical connector that contains the ignition 1 relay coil control circuit. Refer to Engine Control Module (ECM) Replacement .
    3. NOTE: Refer to Test Probe Notice in Cautions and Notices.
  3. Probe the ignition 1 relay coil control circuit at the underhood fuse block with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 8  Go to Step 13 
8
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical.
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 relay coil control circuit. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.
  4. Connect the negative battery cable at the battery.
  5. Probe the ignition 1 relay coil control circuit terminal at the underhood fuse block electrical connector with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 14  Go to Step 17 
9 Measure the resistance from terminal #30 of the ignition 1 relay to terminal #87 with a DMM.
Does the DMM display the specified value?		 infinity ohm Go to Step 10  Go to Step 15 
10 Measure the resistance from terminal #30 of the ignition 1 relay to terminal #86 with a DMM.
Does the DMM display the specified value?		 infinity ohm Go to Step 11  Go to Step 15 
11 Measure the resistance from terminal #85 of the ignition 1 relay to terminal #87 with a DMM.
Does the DMM display the specified value?		 infinity ohm Go to Step 12  Go to Step 15 
12 Test for an intermittent and for a poor connection at the ignition 1 relay location of the underhood fuse block. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Did you find a condition?		 - Go to Step 17  Go to Intermittent Conditions
13 Test for shorted terminals and poor connections at the ECM electrical connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Micro .64 Connectors in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 18  Go to Step 16 
14 Repair the short to voltage in the ignition 1 relay coil control circuit between the underhood fuse block electrical connector and the ECM electrical connector. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 18  -
15 Replace the ignition 1 relay. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) in Wiring Systems.
Did you complete the replacement?		 - Go to Step 18  -
16 Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 18  -
17 Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.
Did you complete the replacement?		 - Go to Step 18  -
18
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition, with the engine OFF.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze/Frame Failure Records.
Did the DTC fail this ignition?		 - Go to Step 3  Go to Step 19 
19 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information System OK
scientia non olet · About LEMON Manuals