P05C8 code meaning
Economy Mode Switch Circuit Range/Performance
What P05C8 means
The economy mode switch selects a fuel-saving mode (flatter pedal map, earlier upshifts, sometimes reduced A/C). It is usually a resistor ladder with 5 V reference read by the engine module; CARB names a driver-selectable eco mode as an off-cycle technology whose use must be counted. GM reports the same switch with its own codes P159F/P15A0, type B with warning lamp after two trips; P05C7–P05CA appear in no manufacturer document available to us. P05C8 means the signal is in range but implausible – between valid ladder steps or permanently pressed; GM accepts a press only for 0.094–1.5 s.
P05C8 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P05C8
- Eco mode switching unintentionally or not at all
- Indicator flickering or off
- Usually no check engine light
Common causes of P05C8
- Most likelySwitch stuck (permanently pressed)
- PossibleContact resistance or corrosion shifting the voltage step
- Less likelySoftware
- Less likelyModule input
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Economy mode switchSwitch wiringEngine control module
What each part of P05C8 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| C8 | The exact fault in that area. |
What to do next
- Note P05C8 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P05C8
What does P05C8 mean?
P05C8 means "Economy Mode Switch Circuit Range/Performance". The economy mode switch selects a fuel-saving mode (flatter pedal map, earlier upshifts, sometimes reduced A/C). It is a generic code, so it means the same on every make.
Is it safe to drive with P05C8?
P05C8 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P05C8 fail an emissions test?
P05C8 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P05C8 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P05C8 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.