Scan Tool Testing and Procedures

SCAN TOOL DIAGNOSTIC CAPABILITIES
The Tech 1 scan tool (or equivalent) has several positions that will indicate the state of the exhaust gases, Heated Oxygen Sensor (HO2S) voltage, short term fuel trim, and long term fuel trim.

NORMAL HO2S VOLTAGE
Normal Tech 1 scan tool voltage varies between 10 mV to 1000 mV (.01 and 1.0 volt) while in "Closed Loop." Diagnostic Trouble Code (DTC) 13 and 63 will set in one minute if voltage remains between 350 mV and 550 mV, but the system will go "Open Loop" in about 15 seconds.

PCM SELF-DIAGNOSIS
The Powertrain Control Module (PCM) self-diagnostic circuit looks for trends in HO2S voltage. If a trend is detected, the Malfunction Indicator Lamp (MIL) (Service Engine Soon) comes "ON."

RICH EXHAUST
A rich exhaust trend causes the sensor voltage to stay above 700 mV for too long. This sets either a:

Code 45 Left (Bank 1) Oxygen Sensor Circuit (Rich Exhaust) Powertrain Controls - ECM/PCM

OR

Code 65 Right (Bank 2) Oxygen Sensor Circuit (Rich Exhaust). Powertrain Controls - ECM/PCM

LEAN EXHAUST
Voltage Below 300 mV
Lean exhaust causes voltage to stay below 300 mV for too long. This sets either a:

Code 44 Left (Bank 1) Oxygen Sensor Circuit (Lean exhaust) Powertrain Controls - ECM/PCM

OR

Code 64 Right (Bank 2) Oxygen Sensor Circuit (Lean Exhaust). Powertrain Controls - ECM/PCM

Voltage Between 350 mV and 550 mV
If voltage stays between 350 mV and 550 mV for too long, the PCM sets either a:

Code 13 Bank 1 (Left) Heated Oxygen Sensor Circuit DTC 13

OR

Code 63 Right (Bank 2) Open Oxygen Sensor Circuit. Powertrain Controls - ECM/PCM

RESPONSE TIME
Not only is it necessary for the HO2S to produce a voltage signal for rich or lean exhaust, it is also important to respond quickly to changes. The PCM senses the response times. If the HO2S responds slowly, the customer may complain of poor fuel economy, rough idle or lack of performance. It may also set false PCM DTCs because the PCM uses oxygen sensor voltages for system checks.