2020 Honda Civic Si electrical system problems

“The headlight electrical wiring on my 2020 Honda Civic Sport sedan, which has 97,000 miles, has experienced deterioration, with the wire insulation disintegrating on one headlight. The Honda dealership inspected the vehicle and confirmed that the wiring insulation is breaking down naturally, not as a result of rodent damage or outside interference. The damaged wiring and headlight connector is available for inspection upon request. This creates a potential safety hazard because deteriorating wire insulation and the blown connector can expose electrical conductors, cause electrical shorts, interrupt headlight operation, and potentially create a fire risk. Headlights are critical for nighttime visibility and ensuring other drivers can see my vehicle, so any loss of headlight function could put me and other motorists at risk. The problem was confirmed by an authorized Honda dealership, which provided an estimated repair cost of approximately $360. The vehicle has been inspected by Honda dealership personnel, who identified the deteriorating wiring and blown connector, recommended repair. There were no known warning lights or dashboard messages before the issue was…”

“On September 27, 2026, at approximately 90,800 miles, the body control module (BCM) in my 2020 Honda Civic Hatchback failed. Symptoms included the alarm sounding on its own, warning lights illuminating on the dash, the vehicle turning its accessories on unprompted while parked (key fob was present), the battery draining, and the key fob intermittently not being recognized.”

“Odometer Fraud. The contact purchased a 2020 Honda Civic. It was discovered that there was a mileage discrepancy. The vehicle was a dealer sale. At the time of purchase, the mileage was 87,000. At the time of registration, it was discovered that the mileage was 247,000.”

“The turbocharger bypass control solenoid valve circuit on my 2020 Civic Si has developed an intermittent open, setting DTC P0035. I diagnosed it myself: the solenoid coil measures 45 ohms and functions when commanded via bi-directional scan tool, and supply voltage is present at the harness connector. However, the control circuit reads approximately 9V in the off state when it should be near ground, and the reading fluctuates when the harness is flexed near the connector — indicating a partial break in the wiring consistent with vibration fatigue. This is a safety concern because the ECM fault cascades to other systems. My scan report shows U0401-68 in the ABS module and U0416-68 in both the EPS and Integrated Driver Assistance modules. The result is that VSA stability control is disabled. I first noticed the problem because warning lights appear during hard cornering — precisely when stability control is most needed. Honda has acknowledged this exact failure mode. Service Bulletin 18-044 (NHTSA ID 10142655), issued June 2018, covers the 2017 Civic Type R for DTC P0035 and states the cause as: heat and the natural frequency of the harness cause the coupler wire…”

“I have owned my vehicle for nearly 18 months and absolutely NO ACTION has been taken on Honda's part to remedy this solution with the capacitor in the circuit board of the front passenger seat weight sensor. Tired of waiting! I want results. This could lead to the front passenger frontal and knee airbags deploying unexpectedly.”

“The air conditioning system in my 2020 Honda Civic EX has a refrigerant leak at the evaporator assembly, causing very weak or almost no cooling even when set to the lowest temperature settings. This happens consistently, including in moderate to hot outside temperatures, making the cabin uncomfortably warm during drives as it could get pretty hot in inland southern California. The A/C evaporator assembly is the failed component, and the part remains in the vehicle available for inspection if requested. This issue creates a safety risk because reduced visibility from window fogging in humid or rainy conditions (due to lack of proper dehumidification and cooling) can impair safe driving. In extreme heat, it also increases driver fatigue and distraction from discomfort. The problem was confirmed by a Honda dealership through diagnostic testing, which identified the evaporator leaking refrigerant. They previously repaired a related condenser leak under warranty, but the cooling issue persisted and was later traced to the evaporator. The vehicle has been inspected by the dealership (manufacturer-authorized) on multiple occasions for this A/C concern. No specific…”