1993 Volvo 850 L5-2.4L VIN 55 B5254SFACTORY OEM SERVICE PROCEDURE

FB. Communication Problems With the Volvo Scan Tools



FB. Communication problems with the Volvo Scan Tools (Diagnostic Key and Volvo System Tester)

Fault-tracing information

Factory service manual diagram




Operating basics

- Normal system voltage (battery voltage)
- Charging system operating normally
- The fault is permanent.

Factory service manual diagram





Defect cause:

- Malfunction in signal cable
- Malfunction in wiring to the Volvo Scan Tools Volvo System Tester Volvo Diagnostic Key.

Fault-tracing starts with FB1.



FB1

Checking communication with other systems


Factory service manual diagram





- Ignition ON.

Check that the Scan Tool ST (Volvo System Tester Volvo Diagnostic Key) can communicate with other systems.

If communication with other system is OK:
- Checking communication with the Transmission Control Module TCM FB2.

If communication with other systems cannot be established:
- Check diagnostic wiring to the Scan Tool ST (Volvo System Tester Volvo Diagnostic Key) for damage.



FB2

Checking communication with the Transmission Control Module (TCM)

Factory service manual diagram





- Ignition OFF
- Ignition ON.

Attempt contact with the TCM using the ST (Volvo System Tester/Volvo Diagnostic Key). CB. Scan Tool Communicates DTMs (Volvo OBD Diagnostic Key)

If communication is established:
- Check the diagnostic wiring to the ST (Volvo System Tester Volvo Diagnostic Key) for loose connections.

If no communication can be established:
- Checking communication with selector cable in the data link connector DLC FB3.



FB3

Checking communication with the adapter cable in the data link connector DLC

Factory service manual diagram





- Ignition OFF
- Ignition ON.

Attempt contact with the TCM using the selector cable in the DLC (A1).

If communication is established:
- Check diagnostic wiring to the Scan Tool ST (Volvo System Tester Volvo Diagnostic Key) for damage.


If there is no communication:

- Fault-tracing as per FC. Communications problems with the Data Link Connector DLC (DLC A). FC. Communications Problems With the Data Link Connector




Factory Service Tools

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When to See a Mechanic

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

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

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