Uploaded July 2026 | Updated September 2026, 3 weeks ago

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In this video, my son Beau and I are diagnosing a Volkswagen with a Bank 1 Sensor 1 O2 heater circuit code, but the real lesson is the bias voltage. That 3.5V signal told me the PCM control wire was intact, the driver circuit was alive, and the heater itself was open.

I’ll show how I confirmed it, and how understanding bias voltage can aid you in future diagnostics!



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0:00 — Intro
0:46 — Bank 1 Sensor 1 heater circuit code
1:08 — Scope and amp clamp setup
1:51 — Wideband vs narrowband O2 sensors
3:23 — Identifying the heater circuit
4:12 — Sensor side vs harness side confusion
5:44 — Amp clamp test on heater wire
6:22 — No heater current found
6:53 — Checking heater voltage
7:13 — 3.5V bias voltage clue
7:41 — Power feed is good
7:51 — Open heater confirmed
8:03 — How the PCM controls the heater
9:48 — Bias voltage and circuit self-testing
11:38 — Test light driver check
13:40 — New O2 sensor installed
14:49 — Rechecking voltage and current
15:42 — Good PWM heater control pattern
16:20 — Test light brightness confirms control
17:20 — Cheese balls for the crows