??There are two types of DTC's, 1 trip DTC's and 2
trip DTC's
??A 1 trip DTC is for a condition that requires
immediate attention such as a catalyst damaging
misfire.
??A 2 Trip DTC is one that a condition must be found
during 2 consecutive trips such as an EGR fault.
??Most Monitors do not set a DTC and light the MIL
when a vehicle fails a test for the first time during a
DRIVE CYCLE. If a test is failed on a second
consecutive DRIVE CYCLE the MIL will light and a
DTC is stored in the vehicles powertrain control
module (PCM).
Step
Action
Values
Yes
No
1
Did you perform the Diagnostic System Check - Vehicle?
--
Go to Step 2
Go to Diagnostic System Check - Vehicle
2
Important: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.
Are any DTCs other than DTC P0172 also set?
--
Go to Diagnostic Trouble Code (DTC) List - Vehicle
Go to Step 3
3
Is the Long Term FT parameter less than the specified value?
-18%
Go to Step 4
Go to Diagnostic Aids
4
?€¢
The air intake duct for being collapsed or restricted
?€¢
The air filter for being dirty or restricted
?€¢
For objects blocking the throttle body
Did you find and correct the condition?
--
Go to Step 9
Go to Step 8
7
?€¢
Ensure that the electrical connectors and wires are secured and not contacting the exhaust system.
?€¢
The HO2S signal circuit for a short to voltage--Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?
--
Go to Step 9
Go to Fuel System Diagnosis
poss
Connect white (test lead) and black (ground lead) wires that are branched from harness approximately eight inches from ECM. After leads are grounded, the "Check Engine" light will flash the diagnostic trouble codes. The DTC's are indicated by the flashing CEL.
FLASH, FLASH, pause, FLASH, FLASH, FLASH = Code 23.
If only one diagnostic trouble code is stored, the DTC will repeat continuously until test leads are disconnected. If more than one diagnostic trouble code is stored, each DTC will repeat three times, starting with the lowest, then proceed to the next DTC. After all DTC's have been displayed, the pattern will repeat.I-MARK 84-85
Connect male and female test leads taped into wire harness near ECM. After leads are connected, the "Check Engine" lamp will flash the trouble codes. The DTC's are indicated by the flashing CEL.
FLASH, FLASH, pause, FLASH, FLASH, FLASH = Code 23.
If only one diagnostic trouble code is stored, the DTC will repeat continuously until test leads are disconnected. If more than one diagnostic trouble code is stored, each DTC will repeat three times, starting with the lowest, then proceed to the next DTC. After all DTC's have been displayed, the pattern will repeat.
86-87 Impulse located near the ECM connector, is used to actuate the Engine Control Module (ECM) trouble code memory within the module. Two terminals (A and C) of this connector are used to activate the diagnostic trouble code system in the ECM. With the ignition switch turned On, engine Off, connect a jumper wire between terminals A and C. The "Check Engine" lamp will begin by flashing a DTC 12. DTC 12 = flash, pause, flash, flash. There will be a longer pause and a code 12 will repeat two more times. This code indicates the self-diagnostic system is operating. The cycle will then repeat until the engine is started or the ignition is switched Off. In most cases, DTC's will be checked with the engine running since no DTC's other than DTC 12 or 51 will be present without the engine running. Remove jumper wire from ALDL connector before starting engine. Reconnect jumper wire after engine is running.
Throttle Body Fuel Injection
The ECM test connection is located under the center console.
A built-in, self diagnostic system will identify problems in the throttle body fuel injection system. When a problem is detected, the diagnostic system will illuminate the "Check Engine" light.
When the engine is started, the Check Engine light should turn off.. If the light remains lit, the self diagnostic has detected a problem. To determine where the problem exists, ground the "Test" terminal of the connector with the ignition On, engine Off and watch the check engine light. Each DTC will flash three times (lowest to highest).
DTC - 42 Ignition bypass circuit error
DTC - 67 AC system low on charge.
READING CODES USING MIL (CHECK ENGINE) LAMP
Be advised that the MIL or CHECK ENGINE light can only perform a limited number of functions and it is a good idea to have the system checked with a scan tool to double check the circuit function.
Fig. Fig. 2: Diagnostic trouble code chart (1 of 2)-1995-97 engines
Fig. Fig. 3: Diagnostic trouble code chart (2 of 2)-1995-97 2.0L engines
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