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Diagnostic Procedure Instructions

Diagnostic Procedure Instructions

The following is an overview of instructions for all 16 categories which may be included in a diagnostic procedure.

Diagnostic Instructions

A link to the Diagnostic System Check - Vehicle is provided here. This procedure should be performed prior to performing other diagnostic procedures, as this prevents misdiagnosis where there are integrated system dependencies.

A link to the Strategy Based Diagnosis is provided here. This provides an overview on how a technician should diagnose a vehicle.

A link to the Diagnostic Procedure Instructions is provided here. This information is an overview of instructions for all 16 categories which may be included in a diagnostic procedure.

DTC Descriptor

Describes what DTCs are diagnosed in this procedure. The DTC number, with Symptom Description when applicable, and descriptor are written out.

Diagnostic Fault Information

The diagnostic Fault Information table identifies each circuit that makes up an electrical subsystem and the associated circuit faults. DTCs and symptoms are listed in the table for all circuit fault modes. This information can be used to diagnose an electrical fault, or as a quick visual aid showing how the different symptoms and DTCs apply for the subsystem being diagnosed.

Even though all the DTCs and symptoms are shown in this table it does not mean they will all be diagnosed in the same procedure.

An example table from an engine coolant temperature (ECT) procedure:

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
ECT Sensor Signal P0117 P0118 P0118 P0125, P0128
ECT Low Reference - P0118 P0118 P0125, P0128


Typical Scan Tool Data

The Typical Scan Tool Data table identifies a scan tool data parameter and its value in reference to potential circuit faults.

An example table from an ECT procedure:

ECT Sensor Temperature - PCM

Circuit Short to Ground Open Short to Voltage
Operating conditions: Engine running Parameter Normal Range: -32 to +130°C (-26 to +275°F)
ECT Signal 140°C (284°F) -40°C (-40°F) -40°C (-40°F)
Low Reference - -40°C (-40°F) -40°C (-40°F)¹
¹ Internal ECM damage may occur if shorted to B+


Circuit/System Description

Circuit/System Description identifies how a circuit/system normally functions.

Conditions for Running the DTC

Conditions for Running the DTC, identifies what conditions must be present to allow the diagnostic to run.

Conditions for Setting the DTC

Conditions for Setting the DTC, identifies the condition(s) that must be present in order to fail the diagnostic and when to set the DTC.

Action Taken When the DTC Sets

Actions Taken When the DTC sets, identifies the default actions taken when a control module sets a DTC.

Conditions for Clearing the DTC

Conditions for Clearing the DTC, identifies the conditions that must be met in order to clear the DTC.

Diagnostic Aids

Diagnostic Aids are suggestions which explain other methods to diagnose the condition. It also provides unique information about the system used to assist the technician in finding and repairing a vehicle condition.

Reference Information

Reference Information includes links providing additional information for the diagnostic procedure.

For example:


• Schematic Reference

• Connector End View Reference

• Description and Operation

• Electrical Information Reference

• DTC Type Reference

• Scan Tool Reference

• Special Tools Required


Circuit/System Verification

The diagnostic format does not force a technician to choose one of the 3 diagnostic categories (Circuit/System Verification, Circuit/System Testing and Component Testing). But, performing Circuit/System Verification first helps the technician determine whether there is a problem in the car. Depending on the test conditions, some diagnostic categories may require another category to be examined first.

This category also serves to route the technician to another diagnostic procedure which should be performed first; for example, a DTC with a higher priority.

Circuit/System Verification is a non-intrusive procedure outlining how to verify that a system or a portion of a system is functioning correctly. During the verification process, the vehicle is kept intact and tested as a complete system. This verification is used to assist the technician in determining whether a condition is current or intermittent. If a condition is deemed intermittent, the technician can use the link in the electrical reference information Testing for Intermittent Conditions and Poor Connections for additional information.

The technician should be able to identify if the fault is occurring on the input circuit - signal or on the output circuit - control when applicable. The technician will need to decide from the verification results if the system is working correctly or if further diagnosis needs to be performed in either Circuit/System Testing and/or Component Testing.

Component codes are used to aid technicians in identifying common components. These codes are the same even if the component names may vary slightly. The codes are found in the wiring diagrams and the diagnostic categories Circuit/System Verification, Circuit/System Testing and Component Testing.

Component Codes

The component codes used in the wiring diagrams consists of a base code with a suffix indicating position or quantity. For example, ABS wheel sensors are indicated with base code (B5) on the wiring diagrams and with position suffix LR, RF, LR or RR as follows:


• B5LF Wheel Sensor (WSS) - Left Front

• B5RF Wheel Sensor (WSS) - Right Front

• B5LR Wheel Sensor (WSS) - Left Rear

• B5RR Wheel Sensor (WSS) - Right Rear


B5 is the base code for wheel sensors and LF, RF, LR and RR indicate the position on the vehicle.

A diagnostic procedure uses the base code (B5) for wheel sensors and the suffix code for position (LR, RF, LR or RR). Example: Ignition OFF, unplug connection at applicable B5 wheel sensor. This formulation indicates all four wheel sensors without indicating position or quantity.

If diagnostics indicate "applicable", the technician will decide which component is indicated by the symptom, which is indicated by RO (driver's door lock not working) or the DTC description (DTC C0585 04: Left Rear Actuator Circuit Open).

Circuit/System Testing

The diagnostic format does not force a technician to choose one of the 3 diagnostic categories (Circuit/System Verification, Circuit/System Testing and Component Testing). But, starting with Circuit/System Verification helps the technician determine whether there is a problem in the car. Depending on the test conditions, some diagnostic categories may require another category to be examined first.

Circuit/System Testing is a step by step, positive-flow, testing sequence which allows the technician to perform each test step, in sequence, until a fault is detected. If the result of a numbered test step is achieved, the normal flow is to proceed to the next numbered test step. If the result of a numbered test step is NOT achieved, the repair arrow bullet (⇒) below that test will identify what actions need to take place.

Intrusive diagnostics are performed to locate the system fault. System harness connections are disconnected from the module or component to test individual circuit functions. The module or component will be used to assist in verifying the circuit function. When a test does not pass, the repair steps (⇒) will indicate what circuit faults to test. For example, short to voltage, short to ground or open/high resistance.

When testing for individual circuit faults, the technician must perform checks on connections, such as connection surfaces and connection voltage, both on the wiring harness and on the component/module. The technician can also use the links in the electrical information reference: Testing for Intermittent Conditions and Poor Connections or Circuit Testing .

The control modules and components will also be diagnosed during these test steps. A retest of a control module or component should always be performed before replacement. For example, re-connect all components and modules and retest the system to verify the condition still exists before replacing modules or components.

Component Testing

The diagnostic format does not force a technician to choose one of the 3 diagnostic categories (Circuit/System Verification, Circuit/System Testing and Component Testing). But, starting with Circuit/System Verification helps the technician determine whether there is a problem in the car. Depending on the test conditions, some diagnostic categories may require another category to be examined first.

Component Testing can offer static and/or dynamic component tests. These tests can be used to verify if a component is operating correctly to avoid unnecessary replacement.

Checks of control modules is not offered in this category. In most cases, the module is used to verify the harness circuits in the Circuit/System Testing category and a retest of the module should always be performed before replacement.

Repair Instructions

Repair instructions have a link to Diagnostic Repair Verification . This link describes how to verify that the fault in the car has been remedied.

All links to Repair or Replacement procedures are located here.

Repair Verification

Repair Verification describes how to verify the vehicle is repaired when additional instructions are needed beyond what is in Diagnostic Repair Verification.