U3511: High Voltage System Interlock Circuit B
Generic fault on the second high-voltage interlock loop (HVIL) circuit. The interlock detects whether HV connectors are properly mated; an open loop forces the HV system into a safe state.
What U3511 means
U3511 is a generic OBD-II network code in the module power group. In plain English: the computer sees a voltage on that circuit that is higher than it should ever be — often an open ground, a short to power, or a failed sensor.
- Check engine light
- Usually on
- Emissions-related
- No
- Limp mode possible
- Yes
- Drive cycle to clear
- Not required
Get it fixed
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Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- 01HV connector not fully matedMost likely
- 02Interlock pilot pin damagedPossible
- 03Gateway module routing CAN messages incorrectlyLess likely
Can I drive with U3511?
Have it checked before relying on the car.
High-voltage faults can shut the drive system down without much warning. Do not open orange high-voltage components; this needs a trained technician.
Why we rate it urgent
- High-voltage system fault: the car may shut down or refuse to start
- Can put the vehicle in limp mode (reduced power)
- Turns on the check engine light
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose U3511
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just U3511. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for U3515, U3519, U351D, U3521. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the hvil loop b and high-voltage connectors for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: HV connector not fully mated; interlock pilot pin damaged; gateway module routing CAN messages incorrectly. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
U3511 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Hard
- Good DIY job?
- Usually a shop job
Involved testing or major parts. Most owners use a shop.
Parts and systems involved
- HVIL loop B
- High-voltage connectors
U3511 FAQ
What does U3511 mean?
U3511 means “High Voltage System Interlock Circuit B”. Generic fault on the second high-voltage interlock loop (HVIL) circuit. The interlock detects whether HV connectors are properly mated; an open loop forces the HV system into a safe state.
Is U3511 serious? Can I keep driving?
We rate U3511 as urgent severity. Have it checked before relying on the car. High-voltage faults can shut the drive system down without much warning. Do not open orange high-voltage components; this needs a trained technician.
What causes U3511?
The most common causes, from most to least likely: HV connector not fully mated; Interlock pilot pin damaged; Gateway module routing CAN messages incorrectly. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix U3511?
Typical labor is about $125–$625 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix U3511 myself?
DIY difficulty is hard. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will U3511 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.