Code
P0038
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Heater Circuit High Voltage Bank 1 Sensor 2
Views:
UK: 11
EN: 43
RU: 15
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the heater control circuit
- Failed/shorted HO2S heater element in Bank 1 Sensor 2
- Corroded/damaged sensor connector or wiring harness
- Aftermarket or internally damaged oxygen sensor
- Blown or incorrect fuse supplying the heater circuit
- Faulty PCM/ECM heater driver (less common)
Symptoms
- MIL/Check Engine lamp illuminated
- Possible failed emissions test or readiness incomplete
- Longer warm-up time for sensor; downstream sensor may not reach operating temperature on schedule
- Possible rough running or decreased fuel economy (usually minor with downstream sensor)
- No obvious drivability symptoms in many cases
What to check
- Read freeze frame and pending codes; confirm P0038 is current and note conditions (engine temp, voltage)
- Visually inspect Bank 1 Sensor 2 connector and wiring for corrosion, pin damage, melted insulation, or water intrusion
- Check related fuses/fusible links for the heater circuit
- With ignition ON (engine off) measure voltage at the sensor harness heater supply terminal and the heater control terminal
- Disconnect the sensor and check harness voltage to confirm if short to B+ is present on the control side
- Measure heater element resistance at the sensor (with sensor disconnected) and compare to specification
Signal parameters
- Battery / ignition voltage (B+): ~12.0–14.5 V (engine running)
- Heater supply (B+) side: near battery voltage (constant fused feed)
- Heater control side (PCM sink) when active: switches to low (near 0 V) or PWM between 0–12 V depending on PCM strategy
- Heater control side when inactive: may be near battery voltage if circuit is open, or float; PCM threshold for high-voltage fault varies by manufacturer
- Typical heater element resistance (downstream O2 sensors): commonly ~2–10 Ω (varies by sensor design)
- Typical heater current draw: roughly 0.5–2 A when fully powered (varies by sensor)
Diagnostic algorithm
- Confirm the code and capture freeze-frame data with a scan tool.
- Visually inspect Bank 1 Sensor 2 connector, harness, and chassis grounds for damage or corrosion. Repair obvious damage.
- Verify fuses/fusible links for the O2 heater circuit; replace if blown and investigate cause.
- With ignition OFF, disconnect the sensor. Measure resistance between the two heater terminals on the sensor. Refer to OEM spec; a very low resistance or near short to battery or ground indicates a bad sensor.
- With ignition ON (engine off), measure voltage at the harness heater supply terminal (should be battery voltage).
- Measure voltage at the harness heater control terminal (PCM side) with the sensor disconnected. If this terminal is showing battery voltage (high) when it should be low or switching, suspect wiring short to B+ or a PCM issue.
- If the control terminal is high with sensor disconnected, backprobe harness and check for a short to B+ by isolating sections of wiring and inspecting connectors or chafing points. Repair wiring as needed.
- If the control terminal behaves correctly when sensor disconnected, connect a known-good sensor (or swap with another downstream sensor if possible) and re-test. If known-good sensor clears the issue, replace the original sensor.
- If wiring and sensor check good but the PCM control output remains incorrect, consider PCM driver fault; verify with a scope and consult manufacturer guidance before replacing PCM.
- Clear codes after repair and perform a drive cycle or confirmed readiness check to ensure the fault does not return.
Likely causes
- Shorted heater control wire to B+ (pin to fused battery feed)
- Damaged or corroded sensor connector allowing voltage bleed
- Internal short in the sensor heater element
- Failed fuse or fusible link supplying O2 sensor heater
- PCM heater driver stuck high due to internal failure
Fault status
Status
P0038 — Heated Oxygen Sensor (HO2S) Heater Circuit High Voltage Bank 1 Sensor 2. The PCM detected an excessively high voltage on the heater control circuit for the downstream O2 sensor on bank 1. Probable causes include a short to battery voltage, a failed sensor heater, wiring/connector faults, a blown fuse, or a defective PCM driver.
Repair difficulty: Medium
Diagnostic time: 1.0-2.0 hours
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