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3.2.8 Non-Monitored Circuits
The PCM does not monitor the following circuits, systems, and conditions even though they could have malfunctions that result in driveability problems. A diagnostic code may not be displayed for the following conditions. However, problems with these systems may cause a diagnostic code to be displayed for other systems. For example, a fuel pressure problem will not register a diagnostic code directly, but could cause a rich or lean condition. This could cause a fuel system, or misfire monitor trouble code to be stored in the ECM.
Engine Timing - The ECM cannot detect incorrectly indexed timing gears.
Fuel Pressure - Fuel pressure is controlled by the fuel injection pump. The ECM cannot detect a clogged fuel pump inlet filter, clogged in-line filter, or a pinched fuel supply.
Fuel Injectors - The ECM cannot detect if a fuel injector is clogged, or if the pintle is sticking.
Fuel Requirements - Poor quality or air in fuel can cause problems such as hard starting, stalling, and stumble.
PCM Grounds - The PCM and ECM cannot detect a poor system ground. However, a diagnostic trouble code may be stored as a result of this condition.
Air Cleaner Air Flow - The PCM and ECM cannot detect a clogged or restricted air cleaner inlet or filter element.
Exhaust System - The PCM and ECM cannot detect a plugged, restricted, or leaking exhaust system.
3.3 Diagnostic Trouble Codes
Each diagnostic trouble code,is diagnosed by following a specific testing procedure. The diagnostic test procedures contain step-by-step instructions for determining the cause of trouble codes as well as no trouble code problems. It is not necessary to perform all of the tests in this book to diagnose an individual code.
Always begin by reading the diagnostic trouble codes using the DRB. This procedure begins in the DTC TEST - Checking the System for Diagnostic Trouble Codes. This will direct you to the specific test(s) that must be performed. Trouble code tests in this manual are organized by scan tool 'P'code number.
3.3.1 Hard Code
A diagnostic trouble code that comes back within one cycle of the ignition key is a "hard" code. This means that the defect is there every time the PCM or ECM checks that circuit or function. Procedures in this manual verify if the trouble code is a hard code at the beginning of each test. When it is not a hard code, an "intermittent" test must be performed.
Codes that are for OBDII monitors will not set with just the ignition key on. Comparing these to non-emission codes, they will seem like an intermittent. These codes require a set of parameters to be performed (The DRBIII pre-test screens will help with this for MONITOR codes), this is called a "TRIP". All OBDII DTCs will be set after one or in some cases two trip failures, and the MIL will be turned on. These codes require three successful, no failures, TRIPS to extinguish the MIL, followed by 40 warm-up cycles to erase the code. For further explanation of TRIPS, Pre-test screens, Warm-up cycles, and the use of the DRBIII, refer to the On Board Diagnostic training booklet #81-699-97094.
Intermittent Code
A diagnostic trouble code that is not there every time the PCM checks the circuit is an "intermittent" code. Most intermittent codes are caused by wiring or connector problems. Defects that come and go like this are the most difficult to diagnose; they must be looked for under specific conditions that cause them. The following checks may assist you in identifying a possible intermittent problem:
Visually inspect related wire harness connectors. Look for broken, bent, pushed out, or corroded terminals.
Visually inspect the related harnesses. Look for chafed, pierced, or partially broken wire.
Refer to any Hotline Newsletters or technical service bulletins that may apply.
Use the DRBIII data recorder or co-pilot.
Reset CounterUse the DRBIII PEP module lab scope.
The reset counter counts the number of times the vehicle has been started since codes were last set, erased, or the battery was disconnected. The reset counter will count up to 255 start counts.
The number of starts helps determine when the trouble code actually happened. This is recorded by the PCM and can be viewed on the DRB as STARTS since set.
When there are no trouble codes stored in memory, the DRB will display "NO DTC'S DETECTED" and the reset counter will show "STARTS since clear = XXX."
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