U3523 High Voltage System Interlock Circuit F Low

U3523 is logged when loop F reads too low, typically from an open plug or a wire shorted to ground. Tracing it means working close to high-voltage parts. The German statutory accident insurance DGUV lets only trained high-voltage staff de-energise the system and insists on the order: isolate, secure against switching back on, then prove absence of voltage with a suitable tester, not a multimeter. Only then open loop F plugs, measure sections or bridge the loop for a test; a bridge must never stay in place, as it defeats the protection. No maker documents U3523. The vehicle stays without high voltage until the cause is fixed.

Likely causes

Symptoms

• Vehicle not ready to drive, high-voltage warning shown
• Charging not possible

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: dguv.de, law.cornell.edu.