Component Tests and General Diagnostics
READING TROUBLE CODESTo read the DTC(s), use a "Scan tool" or ground the diagnostic test terminal, with the engine not running and the ignition "ON". The "Check Engine" malfunction indicator lamp will flash DTC 12 three times and then flash each DTC stored in memory three times. All DTC(s) stored in memory will have been read when DTC 12 is flashed again.
No new DTC(s) can be stored when in the diagnostics test mode (diagnostics lead grounded). This eliminates confusion while the system is being serviced.
CLEARING TROUBLE CODES
To clear the DTC(s) from memory:
^ Ignition "OFF".
^ Disconnect main fuse located in the under hood fuse/relay center near the battery.
SCAN TOOL DIAGMNOSIS
Since the ECM can have a failure which may affect only one circuit, following the diagnostic procedures in this section will determine which circuit has a problem and where it is.
If a diagnostic chart indicates that the ECM connections or ECM is the cause of a problem, and the ECM is replaced, but does not correct the problem, one of the following may be the reason.
^ There is a problem with the ECM terminal connections - The diagnostic chart will say ECM connections or ECM. The terminals may have to be removed from the connector in order to check them properly.
^ The ECM is not correct for the Vehicle - An incorrect ECM may cause a malfunction and may set a DTC.
^ The problem is intermittent - This means that the problem is not present at the time the system is being checked. In this case, refer to the "Symptoms" portion of the manual and make a careful physical inspection of all portions of the system involved.
^ Shorted solenoid, relay coil, or harness - Solenoid and relays are turned "ON" and "OFF" by the ECM, using internal electronic switches called "drivers". Each driver is part of a group of four, called "quad-drivers". Failure of one driver can damage any other driver in the set.
SHORTED OUTPUT
A shorted solenoid, relay coil, or harness in a 1-EFT-SHCI computer will not damage the ECM, but will cause the circuit and controlled component to be inoperative. When the circuit fault is not present or has been repaired, the "quad-driver" will again operate in a normal manner due to its fault protected design. If a fault has been repaired in a circuit controlled by a "quad-driver", the original ECM should be reinstalled and the circuit checked for proper operation. ECM replacement will not be necessary if the repaired circuit or component now operates correctly.
J 34636 or BT-8405 testers or equivalent provide a fast, accurate means of checking for a shorted coil or a short to battery positive voltage.
- The replacement ECM may be faulty - After the ECM is replaced, the system should be re-checked for proper operation. If the diagnostic chart again indicates the ECM is the problem, substitute a known good ECM. Although this is a rare condition, it could happen.
ENGINE CONTROL MODULE (ECM)
A faulty ECM will be determined in the diagnostic charts.
ELECTRONICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY
A faulty electrically erasable programmable read only memory, which is part of the ECM, will set a DTC 51.
ENGINE CONTROL MODULE (ECM) INPUTS
All of the sensors and input switches can be diagnosed by the use of "Scan tool".
Refer to Testing and Inspection under a component for how it can be diagnosed by the use "Scan tool". The "Scan tool" can also be used to compare the values for a normal running engine with the engine you're diagnosing.