Engine Controls - Tests W/O Codes - CNG: Introduction
CAUTION:
When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES
article in GENERAL INFORMATION section before disconnecting battery.
Before diagnosing symptoms or intermittent faults, perform steps in appropriate F - CNG BASIC TESTING and G - CNG TESTS W/ CODES article in the ENGINE PERFORMANCE section below. Use this article to diagnose driveability problems that exist when a hard fault code is not present.
NOTE:
Some driveability problems may have been corrected by manufacturer with a revised Powertrain Control Module (PCM). Check with manufacturer for latest computer application.
Symptom checks can direct the technician to malfunctioning components for further diagnosis. A symptom should lead to a specific component, system test or an adjustment.
Use intermittent test procedures to locate driveability problems that do not occur when the vehicle is tested. Also use these test procedures if a soft (intermittent) trouble code was present, but no problem is found during self-diagnostic testing.
NOTE:
For specific testing procedures, see appropriate I - CNG SYS/COMP TESTS article in the ENGINE PERFORMANCE section. For specifications, see appropriate D - CNG ADJUSTMENTS or C - CNG SPECIFICATIONS article in the ENGINE PERFORMANCE section below.