Onboard Diagnostics
DIAGNOSTIC TROUBLE CODES (DTCs)
9
OBD2 Drive Cycle
- An OBD2 Drive Cycle is an extended set of
driving procedures that takes into consideration the various types of
driving conditions encountered in real life. These conditions may
include starting the vehicle when it is cold, driving the vehicle at a
steady speed (cruising), accelerating, etc. An OBD2 Drive Cycle
begins when the ignition key is turned “On” (when cold) and ends
when the vehicle has been driven in such a way as to have all the
“Enabling Criteria” met for all its applicable Monitors. Only those
trips that provide the Enabling Criteria for all Monitors applicable to
the vehicle to run and complete their individual diagnostic tests
qualify as an OBD2 Drive Cycle. OBD2 Drive Cycle requirements
vary from one model of vehicle to another. Vehicle manufacturers
set these procedures. Consult your vehicle’s service manual for
OBD2 Drive Cycle procedures.
Do not confuse a “Trip” Drive Cycle with an OBD2 Drive Cycle. A
“Trip” Drive Cycle provides the “Enabling Criteria” for one specific
Monitor to run and complete its diagnostic testing. An OBD2 Drive
Cycle must meet the “Enabling Criteria” for all Monitors on a
particular vehicle to run and complete their diagnostic testing.
Warm-up Cycle
- Vehicle operation after an engine off period where
engine temperature rises at least 40°F (22°C) from its temperature
before starting, and reaches at least 160°F (70°C). The PCM uses
warm-up cycles as a counter to automatically erase a specific code
and related data from its memory. When no faults related to the
original problem are detected within a specified number of warm-up
cycles, the code is erased automatically.
DIAGNOSTIC TROUBLE CODES (DTCs)
Diagnostic Trouble Codes (DTCs) are
meant to guide you to the proper
service procedure in the vehicle’s
service manual.
DO NOT
replace parts
based only on DTCs without first
consulting the vehicle’s service manual
for proper testing procedures for that
particular system, circuit or component.
DTCs are alphanumeric codes that are used to identify a
problem that is present in any of the systems that are
monitored by the on-board computer (PCM). Each trouble
code has an assigned message that identifies the circuit,
component or system area where the problem was found.
OBD2 diagnostic trouble codes are made up of five characters:
The 1st character is a
letter
(B, C, P or U). It identifies the
“main system” where the fault occurred (Body, Chassis, Powertrain,
or Network).
The 2nd character is a
numeric digit
(0 thru 3). It identifies the
“type” of code (Generic or Manufacturer-Specific).
Generic DTCs
are codes that are used by all vehicle manu-
facturers. The standards for generic DTCs, as well as their
definitions, are set by the Society of Automotive Engineers (SAE).
Diagnostic Trouble
Codes (DTCs) are
codes that identify a
specific problem area.
