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Home >> Honda Truck >> 1998 >> Passport LX 4WD V6-3.2L DOHC (6VD1) >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Description of On-Board Diagnostics >> DTC Types

DTC Types


Each DTC is directly related to a diagnostic test. The Diagnostic Management System sets DTC based on the failure of the tests during a trip or trips. Certain tests must fail two (2) consecutive trips before the DTC is set. The following are the four (4) types of DTCs and the characteristics of those codes:

- Type A
- Emissions related
- Requests illumination of the MIL of the first trip with a fail
- Stores a History DTC on the first trip with a fail
- Stores a Freeze Frame (if empty)
- Stores a Fail Record
- Updates the Fail Record each time the diagnostic test fails

- Type B
- Emissions related
- "Armed" after one (1) trip with a fail
- "Disarmed" after one (1) trip with a pass
- Requests illumination of the MIL on the second consecutive trip with a fail
- Stores a History DTC on the second consecutive trip with a fail (The DTC will be armed after the first fail)
- Stores a Freeze Frame on the second consecutive trip with a fail (if empty)
- Stores a Fail Record when the first test fails (not dependent on consecutive trip fails)
- Updates the Fail Record each time the diagnostic test fails (Some special conditions apply to misfire and fuel trim DTCs)

- Type C (if the vehicle is so equipped)
- Non-Emissions related
- Requests illumination of the Service Lamp or the service message on the Drive Information Center (DIC) on the first trip with a fail
- Stores a History DTC on the first trip with a fail
- Does not store a Freeze Frame
- Stores Fail Record when test fails
- Updates the Fail Record each time the diagnostic test fails

- Type D (Type D non-emissions related are not utilized on certain vehicle applications).
- Non-Emissions related
- Dose not request illumination of any lamp
- Stores a History DTC on the first trip with a fail
- Does not store a Freeze Frame
- Stores Fail Record when test fails
- Updates the Fail Record each time the diagnostic test fails
Only four Fail Records can be stored. Each Fail Record is for a different DTC. It is possible that there will not be Fail Records for every DTC if multiple DTCs are set.

Special Cases of Type B Diagnostic Tests
Unique to the misfire diagnostic, the Diagnostic Executive has the capability of alerting the vehicle operator to potentially damaging levels of misfire. If a misfire condition exists that could potentially damage the catalytic converter as a result of high misfire levels, the Diagnostic Executive will command the MIL to "flash" as a rate of once per seconds during those the time that the catalyst damaging misfire condition is present.
Fuel trim and misfire are special cases of Type B diagnostics. Each time a fuel trim or misfire malfunction is detected, engine load, engine speed, and engine coolant temperature are recorded.

When the ignition is turned off, the last reported set of conditions remain stored. During subsequent ignition cycles, the stored conditions are used as reference for similar conditions. If a malfunction occurs during two consecutive trips, the Diagnostic Executive treats the failure as a normal Type B diagnostic, and dose not use the stored conditions. However, if a malfunction occurs on two non-consecutive trips, the stored conditions are compared with the current conditions. The MIL will then illuminate under the following conditions:
- When the engine load conditions are within 10% of the previous test that failed.
- Engine speed is within 375 rpm, of the previous test that failed.
- Engine coolant temperature is in the same range as the previous test that failed.

Storing and Erasing Freeze Frame Data and Failure Records
Government regulations require that engine operating conditions be captured whenever the MIL is illuminated. The data captured is called Freeze Frame data. The Freeze Frame data is very similar to a single record of operating conditions. Whenever the MIL is illuminated, the corresponding record of operating conditions is recorded to the Freeze Frame buffer.
Freeze Frame data can only be overwritten with data associated with a misfire or fuel trim malfunction. Data from these faults take precedence over data associated with any other fault. The Freeze Frame data will not be erased unless the associated history DTC is cleared.

Each time a diagnostic test reports a failure, the current engine operating conditions are recorded in the Failure Records buffer. A subsequent failure will update the recorded operating conditions. The following operating conditions for the diagnostic test which failed typically include the following parameters:
- Air Fuel Ratio
- Air Flow Rate
- Fuel Trim
- Engine Speed
- Engine Load
- Engine Coolant Temperature
- Vehicle Speed
- TP Angle
- MAP/BARO
- Injector Base Pulse Width
- Loop Status

Intermittent Malfunction Indicator Lamp
In the case of an "intermittent" fault, the MIL ("Check Engine" lamp) may illuminate and then (after three trips) go "OFF". However, the corresponding diagnostic trouble code will be stored in the memory. When unexpected diagnostic trouble codes appear, check for an intermittent malfunction.
A diagnostic trouble code may reset. Consult the "Diagnostic Aids" associated with the diagnostic trouble code. A physical inspection of the applicable sub-system most often will resolve the problem.





Data Link Connector (DLC)
The provision for communication with the control module is the Data Link Connector (DLC). It is located at the lower left of the instrument panel behind a small square cover. The DLC is 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 out put control tests.
- Reading serial data.
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