About Trouble Codes

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 III.

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 present when the PCM 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/EUROIII 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 DRB III pre-test screens will help with this for MONITOR codes), this is called a "TRIP". All OBDII/EUROIII DTCs will set after two or in some cases one 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 DRB III, refer to the On Board Diagnostic training booklet # 81-699-97094.

Intermittent Code
A diagnostic trouble code that is not present every time the PCM checks the circuit is an "intermittent" code. Most intermittent codes are caused by wiring or connector problems. Intermittents 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 procedures 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 S.T.A.R. Hotline Newsletters or technical service bulletins that may apply.
- Use the DRB III data recorder or co-pilot.

Starts Since Set Counter/Distance Since MIL Set (EURO III)
This reset counter counts the number of times the vehicle has been started since codes were last set or erased. This 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 III as STARTS since set.

When there are no trouble codes stored in memory, the DRB III will display "NO TROUBLE CODES FOUND" and the reset counter will show "STARTS since set XXX."

OBDII/EUROIII vehicles will also display a DTC Specific or Global "Good Trip" counter which will indicate the number of "Good Trips" since the DTC was set. After 3 consecutive "Good Trips," the MIL is extinguished and the good trip counter is replaced by a "Warm Up Cycle" counter. 40 Warm-up Cycles will erase the DTC and Freeze Frame information.

Distance Since MIL Set (EURO III)
The Euro Stage III OBD directive requires that the distance traveled by the vehicle while the MIL is activated must be available at any instant through the serial port on the standard data link connector. This feature works as follows:
1. If the MIL is illuminated due to a fault, the distance count is updated (i.e. it is counting).
2. If there is a stale MIL fault (i.e. the fault is still frozen in memory but the MIL has been extinguished due to 3 good trips), the distance count is held (i.e. frozen).
3. If the distance count is being held due to (Item 2.) and the fault is cleared, the distance is cleared (set to zero).
4. If the distance count is being held due to (Item 2.) and another MIL occurs, the distance count is reset (to 0) and begins updated anew.
5. If a fault occurs while the MIL is already illuminated due to a previous fault (the distance count is updating), then the distance count continues to update without interruption.
6. If the MIL is flashing due to active misfire and there is an active fact (i.e. matured fault for which 3 good trips have not occurred), the distance count behaves as the MIL in ON.
7. If the MIL is flashing due to active misfire and there is no active fault (i.e. the MIL is flashing for a 1 malfunction), the distance count behaves as if the MIL is OFF (because it is not yet a matured fault).
8. The distance count is cleared whenever the fault is cleared. (Via 40 warm up cycles, or via scan tool).

HANDLING NO TROUBLE CODE PROBLEMS
Symptom checks cannot be used properly unless the driveability problem characteristic actually happens while the vehicle is being tested.

Select the symptom that most accurately describes the vehicle's driveability problem and then perform the test routine that pertains to this symptom. Perform each routine test in sequence until the problem is found.

SYMPTOM DIAGNOSTIC TEST

Hard Start Checking The Fuel Pressure
Checking ECT Sensor Calibration
Checking TPS Calibration
Checking MAP Sensor Calibration
Checking the Minimum Idle Air Flow
Checking IAC Motor Operation
Checking EVAP Emission System
Checking IAT Sensor

Engine Stall In Gear Check TCC Operation

Hesitation/Sag/Stumble Checking PCM Power and Ground Ckt
Checking The Fuel Pressure
Checking ECT Sensor Calibration
Checking TPS Calibration
Checking MAP Sensor Calibration
Checking the Minimum Idle Air Flow
Checking IAC Motor Operation
Checking EVAP Emission System

Surge Checking PCM Power and Ground Ckt
Checking The Fuel Pressure
Checking ECT Sensor Calibration
Checking TPS Calibration
Checking MAP Sensor Calibration
Checking the Minimum Idle Air Flow
Checking IAC Motor Operation
Checking EVAP Emission System

Lack of Power/Sluggish Checking PCM Power and Ground Ckt
Checking The Fuel Pressure
Checking ECT Sensor Calibration
Checking TPS Calibration
Checking MAP Sensor Calibration
Checking the Minimum Idle Air Flow
Checking IAC Motor Operation

Poor Fuel Economy Checking PCM Power and Ground Ckt
Checking The Fuel Pressure
Checking ECT Sensor Calibration
Checking TPS Calibration
Checking the Minimum Idle Air Flow
Checking IAC Motor Operation
Checking EVAP Emission System
Checking IAT Sensor