Faulty or sticking economy mode switch or button (worn contacts, dirt or moisture); Wiring damage, chafing or high resistance in the switch signal or ground circuit; Corroded, loose or contaminated connector at the switch or control unit; Switch reference voltage or ground fault from a related circuit or shared supply; Fault in the control unit or body module that reads the switch; Outdated or faulty control unit software where the manufacturer lists it as a known cause.

P05C8

Economy Mode Switch Circuit Range/Performance.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
C8: FaultThe specific fault in that area

What it means

P05C8 is the generic code for an Economy Mode Switch Circuit Range/Performance fault. The control unit that reads the driver's eco or economy mode selector has seen a signal that is implausible, stuck, or does not match what it expects for the switch position or other related inputs. The exact switch type, wiring and which module monitors it vary by model, so check manufacturer data for the specific vehicle.

Symptoms

Eco or economy mode warning or indicator light, or a mode that will not switch on or off
Eco mode stuck on, giving dull throttle response and reduced performance
Eco mode stuck off, so the mode cannot be selected
Malfunction indicator lamp on, possibly with other warnings
Intermittent change of drive mode when driving over bumps or moving the switch

Possible causes

Faulty or sticking economy mode switch or button (worn contacts, dirt or moisture)likely
Wiring damage, chafing or high resistance in the switch signal or ground circuitlikely
Corroded, loose or contaminated connector at the switch or control unitlikely
Switch reference voltage or ground fault from a related circuit or shared supplypossible
Fault in the control unit or body module that reads the switchrare
Outdated or faulty control unit software where the manufacturer lists it as a known causerare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any related drive mode or network codes
Operate the economy mode switch several times and watch whether the displayed or live data state changes correctly
Inspect the switch, its surround and the wiring for moisture, spilt drinks, damage or previous repairs
Check the connectors at the switch and control unit for corrosion, bent pins and poor retention
Using the wiring diagram, check the switch supply, signal and ground for correct voltage and resistance with the switch in each position
Wiggle test the harness while monitoring live data to find intermittent faults
Check the switch itself for correct resistance or continuity in each position against specification
Look for manufacturer service bulletins or software updates relating to this code for the specific model

How to fix

Replace the economy mode switch if it is faulty or sticking
Repair or replace damaged wiring in the signal, supply or ground circuit
Clean, repair or replace corroded or damaged connectors and terminals
Correct any supply or ground fault affecting the circuit
Update or reprogram the control unit software only where an outdated or faulty calibration is a confirmed cause
Replace the control unit only after the switch, wiring and supply have been proven good

Can I keep driving?

Low severity

The car can normally be driven, as the fault mainly affects drive mode selection. Book it in soon, and take more care if the car is stuck in a reduced performance mode.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.