Symptom Related Diagnostic Procedures

Vehicle fails an emission test or vehicle has excessive "rotten egg" smell. Excessive odors do not necessarily indicate excessive emissions.
^ Check:
- EGR valve opening, refer to PCM codes P0401 and P1404.
- Faulty cooling system components (fan, thermostat, PCM sensor).
^ If fuel system is running rich (long term fuel trim less than 118):
- Rich fuel system, refer to PCM Code P0172 and diagnostic chart.
^ If fuel system is running lean (long term fuel trim more than 138):
- Lean fuel system, refer to PCM Code P0171 and diagnostic chart.
^ If emissions test indicates excessive NOx, check for items which cause vehicle to run lean or too hot. Refer to diagnostic chart and emission symptom chart.
^ If emission test indicates excessive HC and CO or exhaust has excessive odors, check for items which cause vehicle to run rich. Refer to diagnostic chart and emission symptom chart, and check for:
- Incorrect fuel pressure.
- Fuel loading of EVAP vapor canister.
- PCV valve plugging, sticking, or blocked PCV hose. Check for fuel in crankcase.
- Three way catalytic converter lead contamination. Check exhaust backpressure and removal of filler neck gas pump nozzle restrictor.
- Improper fuel cap or damaged seal.
- EVAP vapor canister hose connections, condition and routings. Also inspect the vehicle's hood and front of dash seals for damage.
- Faulty spark plugs, wires, coil/module, converter or ignition components.

IMPORTANT: Use of an emissions analyzer may help in locating points of fuel odor emissions. Even small amounts of fuel vapor will cause high levels of hydrocarbons to be indicated by the emissions analyzer. Slowly move the analyzer probe near the suspect area. The hydrocarbon level will increase as the point of emissions is approached. The probe must be moved slowly, as it takes time for the gases to travel through the tester's hose.