Diagnostic Aids
BASIC KNOWLEDGE REQUIREDA basic understanding of hand tools is necessary to perform diagnostic procedures effectively.
NOTE: A lack of basic knowledge while performing diagnostic procedures on the IPC could result in incorrect diagnostic or damage IPC components. Do not attempt to diagnose a IPC problem without this basic knowledge. Without this basic knowledge, you will have difficulty using the diagnostic procedures.
- Basic Electrical Circuits The basic theory of electricity is essential. An understanding of voltage, current and resistance and their relationships to each other will help in the diagnosis of an open or shorted circuit. You must be able to read and understand a schematic wiring diagram.
- Use of Circuit Testing Tools You must know how to use jumper wires to bypass components to test circuits. You must be familiar with essential tool J 39200 DMM or equivalent. You must be able to measure voltage, resistance, and current with the DMM you are using.
AFTERMARKET (ADD-ON) ELECTRICAL AND VACUUM EQUIPMENT
Aftermarket (Add-On) electrical and vacuum equipment is equipment that has been installed on a vehicle's electrical or vacuum systems after the vehicle leaves the factory. This may also include equipment not connected to the vehicle's electrical system such as portable telephones and radios. No allowances have been made in the vehicle design for this type of equipment.
NOTE: Add-on electrical equipment must be connected to the vehicle's electrical system at the battery (power and ground).
Add-on electrical equipment, including telephones and radios, installed to these strict guidelines, may still cause the IPC to malfunction. This may also include equipment not connected to the vehicle's electrical system, such as portable telephones and radios. The first step in diagnosing a IPC problem is to remove add-on electrical equipment from the vehicle. After this is done, if the problem still exists, the problem may be diagnosed in the normal manner.
VISUAL / PHYSICAL UNDERHOOD INSPECTION
One of the most important checks, which must be done before any diagnostic activity, is a careful visual and physical inspection of suspect wiring and components. This can often lead to fixing a malfunction without further steps. An underhood visual and physical inspection can also locate a problem without further steps. Inspect the battery hydrometer (GREEN EYE) to ensure the battery is not discharged. Inspect all electrical circuits for pinches, cuts or disconnects. This visual inspection is very important. It must be done carefully and thoroughly. Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems. The inspection must cover the battery, vacuum hoses, and wiring as follows:
- IPC grounds - dirty, loose and in the wrong location.
- Wiring - loose connections, pinches and cuts.
- VCM / PCM grounds - dirty, loose and in the wrong location.
- Other Class 2 Module grounds.
DIAGNOSTIC INFORMATION
The Diagnostic Trouble Code (DTC) tables in this section are used to locate a faulty circuit or component through the process of elimination. The IPC performs a continual self diagnosis on certain control functions. A DTC will set when a malfunction is detected by the IPC. The IPC will NOT turn the SERVICE ENGINE SOON Malfunction indicator Lamp (MIL) lamp ON. The IPC will turn various Telltales ON which are related to the malfunction detected. Refer to IPC DTC list.
CLASS 2 SERIAL DATA COMMUNICATION
The class 2 network continually monitors various subsystems, (i.e. ATC, BCM, HVAC, IPC, PCM, and VCM) and operating conditions for possible system malfunctions. By comparing system conditions against standard operating limits, certain circuit and component malfunctions can be detected. A five digit alphanumeric Diagnostic Trouble Code (DTC) is stored in the memory of the IPC. When a malfunction is detected by this self diagnostic system. The DTC(s) can later be retrieved by the service technician with a scan tool. The scan tool can aid the technician in repairing various subsystems.
DATA LINK CONNECTOR (DLC)
The sixteen pin DLC is wired to the instrument Panel Cluster and is located under the dash panel on the left side. The DLC connector has terminals that are used to connect to a scan tool. Some common uses of the scan tool are listed below:
- Identifying stored Diagnostic Trouble Codes (DTCs).
- Clearing DTCs.
- Performing output control tests.
- Reading Class 2 serial data.
SCAN TOOL DIAGNOSIS
The Scan Tool can be used to monitor the communications between the TPC and other Class 2 devices. The scan tool can also display IPC data. The IPC DATA LIST, display is under the instrument Panel Cluster selection. This list shows the status of the inputs and outputs to the instrument Panel Cluster. These scan tool values can be very useful in diagnosing the instrument Panel Cluster.
SCAN TOOL INFORMATION MODES
On the scan tool, there are three modes available in the instrument Panel Cluster selection. Select instrument Panel Cluster, then Data List Data.
The following list appears:
- Data
- Inputs
- Outputs
The scan tool allows for the display class 2 values or the state of components commanded by the various systems (i.e. ATC, BCM, HVAC, IPC, PCM, and VCM). The Tests available are dependent upon the system selected, but may include the following:
- Data (Analog Inputs): Displays analog values as seen by the system.
- Inputs (Digital inputs): Displays digital values as seen by the system and provides an indication of whether the input has cycled.
- Outputs (Digital Outputs): Cycles digital outputs controlled by the system OFF/ON for 3 seconds each cycle.
- Special Functions (Analog Outputs): Allows for analog outputs of the system to be set at a desired value.
- Clear Diagnostic Trouble Codes: Will erase all DTC(s) stored for the system currently selected (Note: if the malfunction is still present, the DTC may immediately reset).
THE DIAGNOSTIC EXECUTIVE
The Diagnostic Executive is a unique segment of software which is designed to coordinate and prioritize the diagnostic procedures as well as define the protocol for recording and displaying their results. The Diagnostic Executive also receives diagnostic test results and records the pass and fail status. The main responsibilities of the Diagnostic Executive are:
- Monitoring the Diagnostic Test Enabling Conditions.
- Recording Pending, Current, and History DTC(s).
- Monitoring and Recording Test Status information.
- Recording pass and fail status of test results.
A diagnostic test is a series of steps which has a beginning and end. The result of which is a pass or fail reported to the Diagnostic Executive. When a diagnostic test reports a pass result, the Diagnostic Executive records the following data:
- The fault identified by the diagnostic test is not currently active. When a diagnostic test reports a fail result, the Diagnostic Executive records the following data:
- The fault identified by the diagnostic test is currently active.
- The fault identified has been active since the last 100 ignition cycles or since the codes have been cleared.
- Code supported BIT is enabled.
DIAGNOSTIC TROUBLE CODE (DTC) DIAGNOSIS
This section uses diagnostic tables, wiring diagrams and descriptive text to direct you in performing specific tests to locate and repair the problem. The diagnostic table is a step by step procedure to determine the circuit or component that is the source of the problem. The wiring diagrams and text describing the system, test conditions, failure conditions and actions taken when a DTC is set are located on the page facing the diagnostic table. Diagnostic Trouble Codes (DTC)s, when set, indicate that the IPC has detected a malfunction in a particular circuit or other system. Other system malfunctions are generally, but not exclusively, reported to the IPC via Class 2 data message. The IPC is programmed with routines for internal checks that it follows only under prescribed conditions (called Test Conditions). When these conditions exist, the IPC checks certain circuits or systems for a malfunction. These checks are called failure conditions or conditions for setting the DTC. When these conditions are true, a DTC is set. The IPC may turn a Telltale Malfunction indicator Lamp (MIL) ON. Refer to the Applicable DTC Table for procedures and details.
READING DIAGNOSTIC TROUBLE CODES DTC(S) WITH A SCAN TOOL
The IPC does NOT turn ON the SERVICE ENGINE SOON Malfunction indicator Lamp (MIL). The IPC turns various Telltales ON which are related to the malfunction detected. The recommended method for reading DTC(s) stored in memory, is by using a scan tool plugged into the DLC connector located under the instrument panel on the left side. Follow the scan tool instructions supplied by the tool manufacturer. The DTC(s) will be stored in the memory of the IPC as a Current or a History DTC.
CURRENT CODES
When the IPC determines that the test conditions and failure conditions for a particular DTC are true and it is during the current ignition cycle, it sets the code as a Current DTC. All DTC(s) remain current until the next fault free ignition cycle and the IPC finds the test conditions are true and the failure conditions are false. The Current code then will become a History code only.
HISTORY CODES
When a DTC reports a failure and the failure was not in the current ignition cycle it will be stored as a History Code. The IPC performs internal diagnostic tests to acknowledge that the related systems have reported a pass or fail condition. Each diagnostic test that fails is recorded in the IPC memory. The IPC memory can be accessed with a scan tool to determine which DTC circuit was at fault. A history DTC can be cleared (for any diagnostic test) as follows:
- Completing 100 subsequent ignition cycles with no diagnostic test reporting a fail.
- Using a scan tool.
- Disconnecting the battery.
- Disconnecting the IPC connector.
NOTE: Disconnecting the battery or disconnecting the IPC connector will clear all Current and History IPC DTC(s).
AFTER DIAGNOSIS IS COMPLETE
After diagnosing a problem, in addition to repairing the discovered malfunction, clear any DTC(s) set and verify proper operation. To verify proper operation, you must duplicate the conditions when the customer's complaint occurred or if a DTC was set, you must duplicate the test conditions for that DTC (listed on the facing page of the Diagnostic Trouble Code table) and refer to conditions for setting the DTC. The DTC should not re-set after the repair has been made.
Clearing Diagnostic Trouble Codes DTC(s)
A DTC can be cleared from the memory of the IPC by disconnecting the battery or by disconnecting the IPC electrical connector. A DTC can be cleared from the memory of the IPC by using the Scan tool or after 100 concurrent ignition cycles have occurred without the fault reoccurring. Clearing DTC(s) from the IPC memory is necessary after a repair has been made or to check if a malfunction will occur again. If the fault still exists the DTC will re-set after clearing DTC(s).