P05C9

Symptoms

• Check Engine light is on
• Economy mode is not activated
• Eco Mode button does not function
• No Eco indicator on the dashboard
• Possible slight increase in fuel consumption

Causes

• Short circuit of the signal wire of the switch to ground
• Loss of reference voltage due to broken power wire
• Internal closure of the switch (contacts are shorted to the body)
• Oxidation of connector contacts, creating a parasitic path to ground
• Damage to the wiring in the harness (chafing at the corrugation or fasteners)

How to Fix

1. Read all fault codes with a diagnostic scanner
2. Find the Eco Mode switch and inspect its connector for damage
3. Disconnect the switch connector and measure the reference power voltage - if it is absent, look for a break in the power wire
4. If there is a reference voltage: measure the resistance between the signal wire and ground with the sensor disconnected - a short circuit will indicate damage to the wiring
5. Inspect the wiring harness in the area to the switch, especially in places of kinks
6. Replace the switch or repair the damaged wire

Related codes

Error P05C9 by Vehicle Brand