1, 2 and 3 Digit Codes: 156

Scan Tool 156 (MIL 21):

Trouble Code Number
- Scan tool 156
- General scan tool P0137
- MIL 21

Fault Message
- Downstream HO2S Shorted to Ground

Background
- When the heated oxygen sensor temperature is low, the sensor has the same electrical characteristics as an insulator.
- The heated oxygen sensor output signal line is restricted to 5V. That is why the line voltage is approximately 5V when the heated oxygen sensor temperature is low
- If the heated oxygen sensor output signal line is grounded, its voltage will become low.

Range of Check
- Engine coolant temperature when the engine starts: 49°C (120°F) or less
- Within three seconds after the engine starts

Set Condition
- The heated oxygen sensor output signal line is 0.16V or less.

Probable Cause
- Downstream heated oxygen sensor failed
- Wiring harness and connectors failed
- PCM failed