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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1326 (DATA LINK COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH VCM/PCMTEST DESCRIPTION
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Test Description

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Test Description
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 3:  This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.
  2. 5:  The modules supply a low current (about 1.85 mA) voltage on the serial data circuit. The normal circuit low current will NOT illuminate a test lamp. If the circuit is shorted to battery positive the higher current will illuminate the test lamp.
  3. 7:  This step checks whether the PCM is receiving ignition positive voltage from the EFI relay when the ignition is ON. The PCM cannot provide serial data without ignition positive voltage from the EFI relay.
  4. 8:  If the engine starts and runs, the EFI relay is OK.
  5. 9:  The PCM cannot provide serial data without the correct power and grounds.
  6. 13:  The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Inspect the scan tool for proper operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.
  7. 15:  A shorted sensor reference voltage circuit can cause a loss of scan tool communication with the PCM.
Scan Tool Does Not Communicate with VCM/PCM

Step Action Value Yes No
Schematic Reference: Data Link Connector (DLC) Schematics Engine Controls Schematics in Engine Controls 1.8 L (LV6) orEngine Controls Schematics in Engine Controls 1.8 L (LNK).
1 Did you perform the Diagnostic System Check - Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls In Engine Controls 1.8L (LV6) orDiagnostic System Check - Engine Controls in Engine Controls 1.8L (LNK)
2
  1. Turn ON the ignition, leaving the engine OFF.
  2. Attempt to establish communication with the PCM.
Does the scan tool display the PCM data?		 - System OK Go to Step 3 
3  Attempt to establish communication with the Inflatable Restraint Sensing and Diagnostic Module (SDM).
Does the scan tool display communicate with the SDM?		 - Go to Step 6  Go to Step 4 
4
  1. Disconnect the scan tool.
  2. Measure the voltage from the DLC connector terminal 7 to ground, using a DMM.
Is the voltage more than or equal to the specified value?		 11 V Go to Step 5  Go to Step 10 
5  Connect a test lamp between the DLC connector terminal 7 and ground.
Does the test lamp illuminate?		 - Go to Step 13  Go to Step 14 
6
  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connector containing the serial data circuit.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Measure the voltage of the serial data circuit, on the harness side, with a DMM.
Is the voltage more than or equal to the specified value?		 11 V Go to Step 7  Go to Step 12 
7 
  1. Turn OFF the ignition.
  2. Connect the PCM electrical connector.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Check for system voltage to the PCM from the EFI relay.
Is the voltage more than or equal to the specified value?		 11 V Go to Step 15  Go to Step 8 
8  Start the engine.
Does the engine start and run?		 - Go to Step 9  Go to Ignition Relay Diagnosis in Engine Controls - 1.8L (LNK) or Ignition Relay Diagnosis in Engine Controls - 1.8L (LV6)
9 
  1. Test for an open in the following circuits:
    • The ignition positive voltage circuit between the PCM and the EFI relay.
    • The ground circuits between the PCM and:
    • G104
    • G105
    • G203
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?		 - Go to Step 2  -
10
  1. Test for an open in the serial data circuit between the DLC connector terminal 7 and the right instrument panel junction block.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a repair necessary?		 - Go to Step 2  Go to Step 11 
11
  1. Locate the short to ground in the serial data circuit.
  2. Disconnect each circuit at the right instrument panel junction block one at a time in order to determine which module or serial data circuit is shorted.
  3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?		 - Go to Step 2  -
12 Repair the open in the serial data circuit between the PCM and the right instrument panel junction block. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?		 - Go to Step 2  -
13  Repair the short to battery positive voltage in the serial data circuit. Refer to Wiring Repairs in Wiring Systems. Scan tool damage may have occurred.
Is the repair complete?		 - Go to Step 2  -
14
  1. Verify that all of the following scan tool selections are correct:
    • Model year
    • Carline or Truckline
    • Engine option (VIN)
    • Transmission option
  2. If all the selections are correct and the scan tool does not display any engine data, replace the defective scan tool.
Is the repair complete?		 - Go to Step 2  -
15 
  1. Test the fuel tank pressure (FTP) sensor and the throttle position (TP) sensor reference voltage circuits for a short to ground. Verify that the sensors are not internally shorted.
  2. Repair any faults in the circuits as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a repair necessary?		 - Go to Step 2  Go to Step 16 
16 Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 2  Go to Step 17 
17 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 1.8L (LNK) or Powertrain Control Module (PCM) Replacement in Engine Controls - 1.8L (LV6).
Is the replacement complete?		 - Go to Step 2  -
RENDER: 1.0x

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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.