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1-56 Description and Operation

Powertrain Control Software

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ISO 14229 sends 2 additional bytes of information with each DTC, a failure type byte and a status byte.

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Original table alignment retained · Scroll horizontally if needed

All ISO 14229 DTCs are 4 bytes long instead of 3 or 2 bytes long. Additionally, the status byte for ISO 14229 DTCs is defined differently than the status byte for previous applications with 3 byte DTCs.

Failure Type Byte

The failure type byte is designed to describe the specific failure associated with the basic DTC. For example, a failure type byte of 1C means circuit voltage out of range, 73 means actuator stuck closed. When combined with a basic component DTC, it allows one basic DTC to describe many types of failures.

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Original table alignment retained · Scroll horizontally if needed

For example, P0110:1C-AF means intake air temperature (IAT) sensor circuit voltage out of range. The base DTC, P0110, means IAT sensor circuit, while the failure type byte 1C means circuit voltage out of range. This DTC structure was designed to allow manufacturers to more precisely identify different kinds of faults without always having to define new DTC numbers.

The PCM does not use failure type bytes and always sends a failure type byte of 00 (no sub type information). This is because OBD II regulations require manufacturers to use 2 byte DTCs for generic scan tool communications. Additionally, the OBD II regulations require the 2 byte DTCs to be very specific, so there is no additional information that the failure type byte could provide.

A list of failure type bytes is defined by SAE J2012 but is not described here because the PCM does not use the failure type byte.

Status Byte

The status byte is designed to provide additional information about the DTC, such as when the DTC failed, when the DTC was last evaluated, and if any warning indication has been requested. Each of the 8 bits in the status byte has a precise meaning that is defined in ISO 14229.

The protocol is that bit 7 is the most significant and left most bit, while bit 0 is the least significant and right most bit.

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DTC Status Bit Definitions

Refer to the following status bit descriptions:

Bit 7

• 0 - The ECU is not requesting warning indicator to be active

• 1 - The ECU is requesting warning indicator to be active

Bit 6

• 0 - The DTC test completed this monitoring cycle

• 1 - The DTC test has not completed this monitoring cycle

2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015