U3524High Voltage System Interlock Circuit F High
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3524 indicates a level on loop F above its upper threshold. Pulsed test schemes recognise this easily: if the loop is driven with a fixed square wave, as in Corun's 100 Hz battery design, a wire stuck at 12 V returns a flat level without any edges, which no intact connection could produce. Texas Instruments rates its interlock reference design to survive a direct connection to the 12 V battery, and it offers a third, high-impedance output state for diagnosis. No manufacturer publishes U3524. Look for chafing against fused 12 V wires and for low-voltage plugs in which a loop pin sits right beside a supply pin.
- What you may notice
- High-voltage system remains off, vehicle not ready
- Code returns at once after clearing
- Likely causes
- LikelyLoop F wire chafed against a fused 12 V wire
- PossibleLoop pin bridged to a neighbouring supply pin by corrosion or a bent terminal
- RareSource driver for loop F no longer switches off
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.