Chart 10
NOTE:
Driving styles may have a significant influence on fuel economy. Verify the concern before starting an in-depth diagnosis. The following external factors may contribute to poor fuel economy:
- stop and go driving
- improper tire pressure and size
- vehicle loads (such as trailer towing)
- extended winter warm-up conditions
- high speed driving
- incorrect axle ratio
- road/weather conditions
- aftermarket add-ons
- short run operations
- customer expectations
| SYSTEM/COMPONENT |
REFERENCE (Pinpoint Test unless noted) |
- Check the following PIDs:
- LONGFT1/LONGFT2 (value between -20 and +20%)
- VPWR (value between 10.5 and 17.0 volts, and within 0.5 volt of battery voltage)
|
- LONGFT1/LONGFT2 value low (-):
- Continue diagnosis. Concentrate checks in areas that would cause the engine to run rich.
- LONGFT1/LONGFT2 value high (+):
- Continue diagnosis. Concentrate checks in areas that would cause the engine to run lean.
- VPWR not between 10.5 and 17.0 volts:
- REFER to the appropriate CHARGING SYSTEM - GENERAL INFORMATION
article.
- VPWR between 10.5 and 17.0 volts, but not within 0.5 volt of battery voltage:
- CHECK the B+ voltage to the PCM power relay. CHECK the VPWR circuit between the PCM and the PCM power relay. CHECK the PWR GND circuits.
|
- Verify the engine operates at normal temperature.
|
- Visual. REFER to the appropriate ENGINE COOLING
article
to diagnose any cooling system concerns that are present.
|
- Secondary Ignition System
|
- For vehicles equipped with a coil pack ignition system, refer to PINPOINT TEST JC - Secondary Ignition (Coil Pack)
.
- For all others, refer to PINPOINT TEST JB - Secondary Ignition (COP)
.
|
- Fuel System
|
- refer to PINPOINT TEST HC - Fuel Delivery System
.
|
- Exhaust System
|
- refer to PINPOINT TEST HF - Catalyst Efficiency Monitor and Exhaust Systems
.
|
- Variable Camshaft Timing (VCT) System
|
- refer to PINPOINT TEST HK - Variable Camshaft Timing (VCT)
.
|
- Transmission Fluid Level
|
- Visual
|
- Automatic Transmission
|
- REFER to the appropriate AUTOMATIC TRANSMISSION/TRANSAXLE
article.
|
- PCV System
|
- refer to PINPOINT TEST HG - Positive Crankcase Ventilation (PCV) System
.
|
- Additional Checks:
|
- REFER to the applicable service information article.
|
- Additional Testing
|
- refer to PINPOINT TEST Z - Intermittent
.
|