Network, generic (extended)

U3531 High Voltage System Interlock Circuit K

Check engine lightOn

EmissionsNot relevant

Drive cycleNot required

Limp modePossible

U3531 stands for an unspecified fault on interlock circuit K, the tenth loop. An interlock need not be a dedicated wire pair. For hybrid trucks, International patented running the hybrid CAN bus through the same connector as the power cable: once the plug is parted, data traffic on that bus stops and one terminating impedance drops out, and a traffic detector then opens an interrupter in the high-voltage feed. A loop K built along these lines would react to a dead or disturbed bus section as well as to an open plug, so network faults stored in the same controllers deserve attention. No maker discloses the members of loop K. High voltage stays blocked while the fault is active.

Likely causes

Connector in loop K not fully latched

Communication line routed with loop K interrupted or disturbed

Loop K wiring damaged

Controller monitoring loop K faulty

Symptoms

No ready mode or one high-voltage branch unavailable
Network or communication codes stored alongside
High-voltage system warning in the instrument cluster

Repair estimate

DifficultyHardWorkshop job

Parts and labour€80–1,500

Time0.5–4 h

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

Parts involved

hvil loop khv connectors

Related codes

U3532 U3533 U3534 U352D P0A0A

References: patents.google.com, law.cornell.edu.