P0064 “HO2S (O₂) heater control circuit HIGH — Bank 2 Sensor 3”.

Quick meaning

“Heater control circuit HIGH” means the ECU is seeing a higher-than-expected voltage condition on the heater circuit for the O₂ sensor located at Bank 2, Sensor 3 (usually a downstream/post-cat sensor on the second bank). Typical root causes: wiring shorted to B+ (voltage), failed sensor heater, connector damage, blown/failed ECU driver or fuse/relay.

Safety first

Work with ignition OFF when disconnecting connectors.

Use insulated tools and eye protection.

If you probe with the key ON, avoid shorting pins.

🌟Step-by-step diagnostic checklist (do these in order)

1. Confirm & record

Read the code and freeze-frame with your scanner. Note battery voltage, engine temp and any PIDs.

Verify code is P0064 (or manufacturer variant).

2. Locate the sensor

“Bank 2 Sensor 3” is the 2nd bank (side opposite bank 1) and the 3rd sensor position (usually downstream of converter). Confirm location for the specific engine you’re working on.

3. Visual inspection

Inspect harness and connector for melted insulation, corrosion, soot/soot buildup (exhaust leaks), broken pins, or evidence of heat/repair.

Check for recent exhaust work/aftermarket parts that may have disturbed wiring.

4. Check fuses/relays and chassis grounds

Some vehicles use a fuse or relay feeding heater circuits — check those.

Verify main engine/chassis grounds are tight and corrosion-free.

5. Measure sensor heater resistance (sensor unplugged)

Unplug sensor. Identify the two heater pins (consult a pinout if needed).

Measure ohms across heater pins. Typical result: low single-digit to low tens of ohms depending on sensor — if open/infinite = heater open/faulty sensor.

If resistance is very low (near 0Ω) that could indicate shorted windings or short to ground.

Note: always compare to the OEM spec if available; if you don’t have it, an open = bad, normal small value = OK.

6. Check for short to battery (power short)
With harness disconnected, measure resistance from heater positive pin to battery positive. Low resistance → short to B+ in wiring.

Also measure from heater ground pin to battery positive (should be high/infinite unless shorted).

7. Voltage checks with key ON / heater commanded

Reconnect harness. Backprobe the connector.

Key ON (engine off) — check voltage at the heater positive feed pin. You may see battery voltage if the feed is constant; some systems pulse.

Use your scan tool to command PIDs / force the heater ON (if your tool supports it). While commanded ON: measure voltage on the heater ground wire — the ECU should be switching/grounding the heater.

If you see battery voltage on the ECU ground/driver side when the heater is OFF or un-commanded, there’s likely a short to B+ upstream of the ECU or an ECU fault.

8. Current draw test (if possible)

If you have a clamp meter that reads DC current or a series ammeter, measure heater current while commanded ON. Compare to known good values or to another identical sensor on the vehicle. Excess current can indicate short; no current indicates open or ECU not switching.

9. Wiggle / flex test

With backprobes and heater commanded, wiggle harness and connectors; watch for intermittent changes or code set. This finds broken strands or intermittent shorts.

10. Swap / substitution test
If the other bank has an identical sensor (and wiring lengths make it practical), swap sensors (or unplug and measure) to see if the code follows the sensor or stays with the circuit. If code moves, sensor is bad. If it stays, wiring/ECU is at fault.

11. If wiring short to power is found

Isolate by sections: disconnect connectors along harness to localize the short. Repair/replace damaged section.

12. If wiring and sensor OK but fault persists

Suspect ECU heater driver. Confirm with manufacturer diagnostic (some ECUs expose driver pin voltages or require bench testing). Replacement or reflash may be required — check for Technical Service Bulletins (TSBs) for that model (dealer database).

13. After repaire.

Clear codes, perform a drive cycle or re-run the self-test / freeze-frame monitor. Confirm code does NOT return.

🌟Common causes (order of likeliest to least)

1. Short to battery (B+) in heater wiring (melted/repair splice, chafing)

2. Failed sensor heater element (open or internal short)

3. Connector corrosion / poor ground / loose pin

4. Blown fuse or relay feeding heater circuits

5. ECU driver failure (less common)

6. Software/firmware issue (rare — check TSBs)

Quick troubleshooting summary (one-line checks)

Is the heater element open? → yes → replace sensor.

Is heater control line shorted to B+? → yes → repair wiring.

Does the ECU try to switch the heater (scan tool command)? → no → suspect ECU or upstream wiring/fuse.

Welcome to madurai car service 💐🙏🏻.