P0D18: Battery Charging System A High Voltage Interlock Circuit High

P0D18 flags a charging HVIL signal that sits too high. On the Chevrolet Volt and Cadillac ELR GM tests the loop in two states: with the 5 V source off, a sensed level above 24 % of reference (5 of 6 samples in 2011, 5 of 8 for 2014 and ELR), and with it on, a level above 44 % (4 of 6), set the code as Type A, MIL after one trip. A high value may point to a break or added resistance in the loop or a short to a voltage. Polestar stores P0D1800 in the BECM of the 2021–2023 Polestar 2 with a propulsion warning and resolves it with BECM software 2.10 (TJ 36713). Kia lists P0D1812 for the 2023 Niro EV among the codes that lead to ICCU replacement (bulletin 298). The low case is P0D17, the open loop P0D15.

Symptoms

• Malfunction indicator lamp (GM Type A)
• Propulsion or high-voltage warning in the cluster
• Slow or no AC charging

Most likely causes

• High resistance or partial break in the interlock loop
• Battery module software needing an update (Polestar 2)
• Faulty integrated charging unit (Kia Niro EV ICCU)
• Interlock wire shorted to a voltage source

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

Good to know

• It can trigger limp mode.

What each character of P0D18 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• D: Subsystem depends on the code range
• 18: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0D18?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0D18?

The most common causes are: high resistance or partial break in the interlock loop; battery module software needing an update (Polestar 2); faulty integrated charging unit (Kia Niro EV ICCU).

Related codes

• P0D15Battery Charging System A High Voltage Interlock Circuit/Open
• P0D16Battery Charging System A High Voltage Interlock Circuit Performance
• P0D17Battery Charging System A High Voltage Interlock Circuit Low
• P0D19Battery Charging System A High Voltage Interlock Circuit Intermittent/Erratic
• P0A0DHigh Voltage System Interlock Circuit A High

Sources

• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• gsi.ext.gm.com: 16OBDG01 Hybrid Diagnostics
• static.nhtsa.gov: MC 10242241 0001
• static.nhtsa.gov: MC 10242579 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.