Blue Bird bus yellow check engine light, code p0155

Exhaust System
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Blue Bird bus yellow check engine light.
Scan for codes:
p0155 - 02 sensor heater bank 2 sensor 1

Possible cause: High resistance or open circuit.

The P0155 code indicates a problem with the oxygen sensor heater circuit on Bank 2, Sensor 1, meaning the engine control module (ECM) detects a short or excessive resistance in the heater circuit of that specific oxygen sensor.

Here’s a breakdown of what the P0155 code means and potential causes and fixes:

What the P0155 Code Means:

  • DTC (Diagnostic Trouble Code):

P0155 stands for “O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)”.

  • Location:

Bank 2 refers to the side of the engine opposite of Bank 1 (often cylinder number 2), and Sensor 1 is usually the upstream oxygen sensor, located before the catalytic converter.

  • Problem:

The ECM detects an issue in the heater circuit of the oxygen sensor on Bank 2, Sensor 1, such as a short circuit or excessive resistance.

  • Symptoms:

Possible symptoms include rough idling, rough running, and a check engine light.

Possible Causes:

  • Faulty Oxygen Sensor:

The oxygen sensor itself could be faulty, particularly the heater circuit.

  • Wiring Issues:

Problems with the wiring harness or connections to the oxygen sensor can cause shorts or resistance issues.

  • Poor Connections:

Loose or corroded connections in the wiring harness can lead to a faulty circuit.

  • Engine Coolant Temperature Sensor Issue:

In some cases, a faulty engine coolant temperature sensor can also trigger this code.

Troubleshooting and Fixes:

  • Check the Oxygen Sensor: Visually inspect the oxygen sensor for any damage or loose connections.

  • Inspect Wiring: Carefully check the wiring harness and connections for any signs of damage, shorts, or corrosion.

  • Replace the Oxygen Sensor: If the oxygen sensor is faulty or damaged, replace it.

  • Repair Wiring: If wiring issues are found, repair or replace the affected wiring harness or connections.

In this case, my resolving process:

  1. R&R O2 sensor. I replaced the left front O2 sensor. Clear the code, road test, the yellow check engine light not show on the road test. But when I start the bus, the yellow check engine light show again.

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  2. Check voltage. There are five wires to left oxygen sensor, grey, black, white, blue and yellow. Start the bus, check voltage, grey 3 to 0.06V, black ground, white 3.1 to 3.13v, blue 15.25v, yellow 0, The problem is the wire to yellow (O2 sensor) broken. Reconnect the wire, also replaced the pigtail.

  3. Road test. Clear the codes, road test, shut down and start the bus. The yellow check engine light not show again.