DTC P013700 – O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

Bank 1 Sensor 2 = Post-Cat Oxygen Sensor (after catalytic converter)

✅ Meaning

The ECM sees very low voltage from the post-catalytic O₂ sensor (usually below 0.1V).
This sensor monitors catalytic converter efficiency.

✅ Common Causes

Most common in workshops

1. Exhaust leak before Sensor 2

2. Damaged O2 sensor (B1S2)

3. Wiring issues

Broken signal wire

Signal short to ground

Poor connector contact

4. Low voltage supply to heater circuit

5. Catalytic converter not functioning well (rare)

6. Contamination of sensor

Coolant leak

Oil burning

Fuel additives

🔧 Step-By-Step Diagnostic Procedure

🌟 Check live data

Look at Bank 1 Sensor 2 voltage:

Normal: 0.6–0.8V stable

Low voltage code: 0.00–0.10V, stuck low

If B1S2 is flat 0.00V, suspect wiring or bad sensor.

🌟Visual inspection

Check:

Sensor 2 wiring touching exhaust

Melted harness

Corroded connector

Loose plug

Fix if damaged → clear code → retest

🌟 Check exhaust leak

Inspect flex pipe, flange, catalytic converter joint.
If there is a leak before sensor 2, it pulls in outside air → low voltage.

🌟 Check power & ground

Using multimeter at B1S2 connector:

Heater power: 12V with ignition ON

Ground: continuity to chassis

Signal wire: should not have short to ground

If no 12V → check fuse / relay for O2 heater.

🌟 Replace O2 sensor if needed

If:

Heater is working

Wiring is good

No exhaust leak

Signal still stuck low

Then replace Bank 1 Sensor 2.

Use OEM quality (NTK/NGK or Bosch). Cheap sensors fail often.

🛠️ Final Quick Repair Summary

Step Action

1 Scan → check B1S2 live voltage
2 Inspect wiring & connector
3 Check exhaust leaks
4 Confirm heater power supply
5 Replace O2 Sensor (if sensor stuck low)

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