Dodge Nitro: Onboard diagnostic system — OBD II
Your vehicle is equipped with a sophisticated Onboard Diagnostic system called OBD II. This system monitors the performance of the emissions, engine, and automatic transmission control systems. When these systems are operating properly, your vehicle will provide excellent performance and fuel economy, as well as engine emissions well within current government regulations. If any of these systems require service, the OBD II system will turn on the “Malfunction Indicator Light (MIL).” It will also store diagnostic codes and other information to assist your service technician in making repairs. Although your vehicle will usually be drivable and not need towing, see your authorized dealer for service as soon as possible.
CAUTION:
• Prolonged driving with the MIL on could cause
further damage to the emission control system. It
could also affect fuel economy and drivability. The
vehicle must be serviced before any emissions
tests can be performed.
• If the MIL is flashing while the engine is running,
severe catalytic converter damage and power loss
will soon occur. Immediate service is required.
Loose Fuel Filler Cap Message
If the vehicle diagnostic system determines that the fuel filler cap is loose, improperly installed, or damaged, a “gASCAP” message will display in the odometer or a “CHECK GASCAP” message will be displayed in the Electronic Vehicle Information Center (EVIC). Refer to “Electronic Vehicle Information Center (EVIC)” in “Understanding Your Instrument Panel” for further information. Tighten the gas cap until a clicking sound is heard. This is an indication that the gas cap is properly tightened. Press the odometer reset button to turn the message off. If the problem persists, the message will appear the next time the vehicle is started. This might indicate a damaged cap. If the problem is detected twice in a row, the system will turn on the MIL. Resolving the problem will turn the MIL light off.
See also:
If the engine overheats
If your temperature gauge indicates overheating,
you experience a loss of power, or hear loud
pinging or knocking, the engine is probably too
hot. If this happens, you should:
1. Pull off the road and stop as soon as it is safe
to do so.
2 ...
ENGINE COMPARTMENT — 3.7L
1 — Air Cleaner Filter.
6 — Washer Fluid Reservoir.
2 — Engine Oil Dipstick.
7 — Engine Coolant Reservoir.
3 — Brake Fluid Reservoir.
8 — Engine Oil Fill.
4 — Integrated Power Module.
9 — Coolant Pressure Cap.
5 ...

ENGINE COMPARTMENT — 3.7L