Introduction

Introduction




Volvo has developed a wide range of tools and information for easier and faster troubleshooting of the vehicle and its different systems. The range includes service and troubleshooting information, integrated self-diagnostics in control modules, measuring instrument for exhaust analysis, diagnostic tools, etc.
Troubleshooting or diagnostics are performed by the mechanic using two different concepts; Off Board Diagnostics (diagnostics outside the vehicle) or On Board Diagnostics (diagnostics system in the vehicle).
Off Board Diagnostics (diagnostics outside the vehicle) is done without help from the control module's self-diagnosis. Examples of these are:
- Breakout box and multimeter to measure signals.
- Mechanic's troubleshooting using hearing, touch, and vision as well as experience.
- Diagnostic tools that are connected in parallel between control module and connector.
- Cylinder leak tester.
On Board Diagnostics (diagnostic systems in the vehicle) is done using the control module's self-diagnosis and is read out and presented using a diagnostics tool.









The term Diagnostics refers to true recognition and designation of an illness. The term comes from the Greek dia = through, and gnosis = knowledge. The purpose of a diagnosis is to give a summarized term for the different symptoms that the "sick" describes, and thus be able to give a specific treatment.
The control module in the vehicle includes software to manage intended function (e.g., control all functions of an engine), to monitor the system's components and functions. Monitoring (self-diagnosis) detects any malfunctions, stores these, activates protective actions (back-up modes) and, in some cases, warns the driver.
Monitoring (diagnosis) is always activated when the system is on but tests are started and run according to different pre-defined conditions. A malfunction that is detected is first assessed by monitoring, after, e.g., a certain time, a certain number of driving cycles, certain driving/operation cases or other conditions, the control module decides if it is a real malfunction or not. When monitoring determines that a real malfunction exists, it can be said that the malfunction is confirmed and the malfunction is stored.
The basic goal of self-diagnosis in control modules is to detect and report malfunctions in a control module or its connected components and cables. Part of the goal (found in legal requirements) is also to detect malfunctions that affect emissions as well as malfunctions that may cause subsequent damage to emission-related components.
Self-diagnosis shall also warn for malfunctions that mean a safety risk for drivers, passengers, and vehicles that otherwise would not cause a symptom and thus not be detected. This applies to, e.g., brake system and SRS-system.
Self-diagnosis shall be used by workshops as one of the tools for taking care of the symptom (property/malfunction) that the customer experiences. After the malfunction cause is found (via troubleshooting) and taken care of (via repair), self-diagnosis can also be used to verify that the malfunction cause has been fixed and that the customer's symptom does not exist any longer.

Note! The control module's self-diagnosis (diagnostic trouble code tests) cannot detect all malfunctions that may occur in a vehicle. This primarily applies to mechanical malfunctions but also some electrical malfunctions, e.g., poor connection to battery, or relay spools for a relay are monitored but the function/circuit that the relay controls is not monitored. Unfortunately, sometimes the control module's self-diagnosis can miss to generate a diagnostic trouble code for a malfunction where the customer experiences a symptom (malfunction), and sometimes it may generate a diagnostic trouble code despite the customer not experiencing any symptom (malfunction). This is because customers have different sensitivity to malfunctions (how easily the symptom is detected) and because it is not always to optimize self-diagnosis for all conditions that may occur during the vehicle's life.That is why you should not entirely rely on the vehicle's diagnostic trouble codes. Diagnostic trouble codes should only be regarded as indicators of probably malfunction sources. If the customer experiences a symptom (malfunction) but diagnostic trouble codes are not stored, this does not mean that the vehicle is trouble-free!

Worth keeping in mind when troubleshooting:
- When there is so much electronic equipment in the vehicles, it is easy to blame the "complex" electronics and forget the normal basics for, e.g., an engine's function. But the basics are the same today as when we had carburetor engines!
- A common mistake in troubleshooting is to quickly restricting yourself to a certain area without having checked basic functions, e.g., that the ignition system and engine are in good mechanical condition, the battery is fully charged, fuses are intact.
- Troubleshooting information gives very good guidance when troubleshooting and is almost impossible to do without. By using the customer's symptom, developed troubleshooting methods with, e.g., diagnostic trouble code information, you are quickly guided to being able to pin-point the malfunction.

Note! The electronic components in the control systems are very reliable and seldom cause any malfunctions.

This document describes the following:
- Background to why self-diagnosis is found in the vehicle.
- Diagnostic services, what they do.
- Using the self-diagnosis.
- Diagnostic versions and its communication method.
- Tools for reading out diagnosis.
- Where I find the information.