Network, generic (extended)

U3525 High Voltage System Interlock Circuit G

Check engine lightOn

EmissionsNot relevant

Drive cycleNot required

Limp modePossible

U3525 stands for a fault on the seventh interlock loop, circuit G, that the module does not classify further. Auxiliary high-voltage consumers are candidates for loops of their own: Sanden runs an interlock loop beside the HV plug between an electric A/C compressor and the traction battery, and a Chinese design cited by Caterpillar links an air-conditioning interlock circuit to the main one over CAN. On Mercedes model line 243 the PTC heater's control unit logs its own interlock code, P154700. Which consumer sits on loop G is not public. A dead loop G may only disable heating or cooling, or may block the whole system.

Likely causes

HV plug of an auxiliary consumer such as compressor or heater not latched

Loop G wiring to the auxiliary consumer damaged

Interlock contacts inside the consumer's connector damaged

Evaluating controller faulty

Symptoms

Air conditioning or electric heater unavailable
In some designs no ready mode at all
High-voltage or climate warning in the 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 ghv connectors

Related codes

U3526 U3527 U3528 U3521 P0A0A

References: patents.google.com, patents.google.com, static.nhtsa.gov.