Reading Diagnostic Trouble Codes

PRE-TEST CONDITIONS:

Prior to performing a self-diagnosis or testing of the system, make sure that all other related systems that can affect the operation of the ECI System have been checked and determined to be functioning properly.
Also, ensure that the battery is fully charged, as detection of input signals cannot be made when battery voltage is low. If the battery requires charging, perform a slow charge without disconnecting the battery cables. Disconnecting the battery cables for more than 10 seconds will erase all the current fault codes from the ECU memory.
Ensure all harness connectors are clean and securely connected. If wiring repairs are necessary, replacement wiring should be of the same type to prevent ignition and radio interference. Shielded wire is used between the ECU and ignition coil negative pole, as well as the body ground strap.

Fig. 11 ECI diagnostic test connector.:

EXTRACTING CODES:

Turn ignition switch to the ``Off'' position. Connect a voltmeter between ``self-diagnosis output'' and ``ground'' terminals of connector, Fig. 11, located in the engine compartment.

Fig. 12 Self diagnosis signal indicating system is normal:

Fig. 13 Self diagnosis signal indicating a system malfunction:

Turn ignition switch ``On.'' An indication of ECU memory will immediately begin. Input signal malfunctions are indicated by voltmeter pointer deflection. If the system is in the normal condition, voltmeter will read a constant 12 volts, Fig. 12. When input signal is abnormal, pointer deflection alternates between 0 volts and 12 volts every .4 seconds with a 2 second lag between each abnormal code. For example, pointer deflection between 0 volts and 12 volts eight times every .4 seconds with a two second lag, then repeated, indicates code 8; pointer deflection between 0 volts and 12 volts twice for .4 seconds with a two second lag, then repeated, indicates code 2. The diagram shown, Fig. 13, indicates codes 2 and 5 are abnormal.



Malfunctions can be identified by observing pulses on voltmeter and comparing them to the ECI diagnostic chart. After recording each malfunction, repair as necessary items listed in ``check item'' column in diagnostic chart. Turn ignition switch ``Off.'' Disconnect battery ground cable to erase codes from computer memory, then road test vehicle and ensure all malfunctions have been repaired.