DESCRIPTION SERVICE MANUAL NUMBER 22
Page 5A-30 90-860074--1 FEBRUARY 2002
Diagnosis and Testing
NOTICE
For more information on diagnosis and testing refer to SECTION 5E.
ECM Reactions During Operation
The ECM is capable of performing diagnostic checks within the electronic diesel fuel
injection system. When the ECM senses a problem in the system it will identify the
problem(s) by storing fault code number(s) in its memory. The fault code number(s) can be
retrieved from the ECM memory and can be used to identify the improperly operating circuit
or component.
There are two recommended methods of retrieving fault codes from the ECM:
1. Scan Tool
2. Blink Code Tool
ECM Self-Diagnostics
The ECM performs a continual self-diagnosis on certain control functions. This diagnostic
capability is complemented by the diagnostic procedures contained in this manual. The
ECM’s language for communicating the source of a malfunction is a system of diagnostic
codes. The codes are four digit numbers preceded by the letter P. The prefIx letter P is the
abbreviation for Powertrain, an internationally standardize reference. When a malfunction
is detected by the ECM, a code is set and the Malfunction Indicator Lamp (MIL) is illuminated
in most instances.
NOTE: On factory instrumentation the MIL is a lamp with a check mark (n) on the colored
lens.
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