P1137 MERCURY – Lack of Heated Oxygen Sensor Switches The Bank 1 Sensor 2 Switch Indicates Lean

Possible Causes

1. Exhaust gas leaks
2. Faulty Heated Oxygen Sensor 2 (HO2S2) (downstream), Bank 1
3. Open or short circuit in Bank 1 Heated Oxygen Sensor 2 wiring harness
4. Poor electrical connection in Heated Oxygen Sensor 2 circuit, Bank 1
5. Inappropriate fuel pressure
6. Faulty fuel injectors

How to Fix MERCURY Code P1137?

Start by checking the possible causes listed above:

• Visually inspect the wiring harness and corresponding connectors.
• Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

Possible Symptoms

• Check Engine Light on (or Service Engine Soon warning light)

Meaning of MERCURY Code P1137

The Heated Oxygen Sensor 2 (HO2S2), located after the three-way catalyst (manifold), monitors the oxygen level in the exhaust gases on each engine bank.

For optimal catalyst operation, the air-fuel ratio must remain close to the ideal stoichiometric ratio. Here’s how it works:

• The HO2S2 generates a voltage between 0.1 and 0.9 V in response to oxygen in the exhaust gases.
• If oxygen in the exhaust gases increases, it indicates a lean mixture. The PCM interprets this when the HO2S2 voltage is below 0.45 V.
• If oxygen in the exhaust gases decreases, it indicates a rich mixture. The PCM interprets this when the HO2S2 voltage is above 0.45 V.

The PCM then adjusts the fuel injection time to maintain an air-fuel ratio as close as possible to the optimal stoichiometric ratio.