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:
- Faulty cooling system components (fan, thermostat, ECM1 sensors).
^ If fuel system is running rich (long term fuel trim less than 118):
- Rich fuel system, refer to DTC P0172, P0175 and diagnostic chart.
^ If fuel system is running lean (long term fuel trim more than 138):
- Lean fuel system, refer to DTC P0171, P0174 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, emission symptom chart and check for:
- Incorrect fuel pressure.
- Fuel loading of EVAP canister.
- Three way catalytic converter lead contamination. Check exhaust backpressure, and check for 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, coil/module, converter, ignition components or misfire.

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.

^ Perform "Diagnostic Circuit Check."

IMPORTANT:
^ IF EMISSION TEST shows excessive CO and HC, check items which cause car to run rich (Long Term Fuel Trim less than 110). Refer to "Diagnostic Aids" of DTC P0172.
^ IF EMISSION TEST shows excessive NOx, check items which cause car to run lean or too hot.

^ CHECK: For vacuum leaks.
^ CHECK: For lead contamination at catalytic converter (look for the removal of fuel filler neck restrictor).
^ CHECK: Carbon build-up. Remove carbon with top engine cleaner. Follow instructions on can.
^ CHECK: Spark plugs, and ignition components.
If the Scan tool indicates a very high coolant temperature and the system is running lean:
^ CHECK: Engine coolant level.
^ CHECK: Engine thermostat for faulty part (always open) or for wrong heat range.

IMPORTANT: If the system is running RICH (check valves), refer to "Diagnostic Aids" of DTC P0172 and/or P0174. If system is running LEAN refer to "Diagnostic Aids" of DTC P0171 and/or P0175.

^ CHECK: For properly installed fuel cap.
^ CHECK: Fuel pressure.
^ CHECK: Injector balance test.
^ CHECK: Canister for fuel loading.