When DEQ fails a vehicle at their emissions testing facility, it’s usually for one of three reasons: High emissions that have actually been measured; failed equipment as indicated by the check engine light (also called malfunction indicator light or MIL); or visible smoke.

We have some of the most competent and experienced diagnosticians available to diagnose what your Toyota, Lexus, or Scion needs to pass DEQ.

The following DEQ checklist is a composite description that describes DEQ diagnostic procedures for vehicles with several generations of developments, including:

• Fuel injected.
• With air-fuel ratio feedback by way of O2 sensors and/or air-fuel ratio sensors.
• Vehicles with catalytic converters.
• Electronically controlled timing.
• Ignition systems with distributors and distributorless ignition systems with ignition coils directly over the spark plugs.
• Vehicles with first-generation onboard diagnostics (OBD1) that are accessed through jumper wires and blinking-light codes; and vehicles with second-generation diagnostics (OBD2) that are accessed through full computer hook-up.

Our DEQ testing procedures include any number of the steps listed below, not necessarily in this exact order:

• Test drive for drivability symptoms.
• Check for stored diagnostic trouble codes.
• Check Toyota’s online database to see if any bulletins have been published that apply.
• Check actual emissions if appropriate and compare to DEQ test results.

Check various systems:

• Check air/fuel ratio system feedback operation.
• If equipped with air fuel ratio sensor, verify that it’s giving credible signals that reflect changes of mixture that you impose on the system.
• If equipped with O2 sensor, note whether:
  • Active back and forth over mid range.
  • If not, is computer responding to O2 sensor signal? Can quickly test by giving artificial signals (positive and negative) by passing battery voltage through your body to the computer through the O2 sensor circuit.
  • Able to give full range of signal (nearly 0 volts when made lean, and nearly 1 volt when made rich).
  • Can quickly register changes, from very lean to rich and back again.
• Are devices getting computer’s switching signals?
• Are devices working?
• Air injection/suction system working?
• Check Vf1 voltage at idle and at higher rpm’s. Voltage ranges from 1-5. Low voltage indicates computer compensating to make leaner, and high voltage indicates computer compensating to make richer. Mid range means no compensation needed. For OBII, check fuel trim.
• Check initial ignition timing if applicable.
• Note whether it pings on test drive. (NOx related)
• Check EGR. (NOx related)
• Has vacuum signal to EGR valve when accelerating?
• If no, does vacuum modulator have pressure signal from EGR tube and a vacuum signal?
• Valve opens and causes engine rpm to drop significantly when given vacuum signal at idle?
• Valve doesn’t stick open and cause a miss at idle? (HC related)
• Check Catalytic Converter
• Note emission readings at idle and 2500 rpms.
• Note how much readings flare up on transitions between rpms.
• Note how high HC readings go on a snap, full-throttle acceleration
• Note whether idle readings that improve initially after revving for awhile increase again after a few minutes of idling
• Note cat temp at inlet and at outlet. Should at least maintain temp, and preferably should increase.
• After cat is fully activated, note CO2 readings on a dead crank test. Should be 12% or better.
• Check for visible smoke when revving after prolonged idling as possible indication of oil burning.
• Pull a spark plug & check condition. (Worn or fouling?)
• Check appropriate tune items.
• Exhaust leaks? (Dilution)
• Retest emissions and/or components after work completed.
• Test drive car again after work completed.