Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P05CA Economy Mode Switch Circuit High

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

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. P05CA means the switch circuit voltage is too high – a short to positive or, with a resistor ladder, an open switch ground pulling the signal to the 5 V reference; GM's equivalent is P15A0. GM's test values: reference 4.8–5.2 V, signal at rest 0.06–0.25 V.

Likely causes

Switch ground open
Signal line shorted to positive
Switch faulty
Module

Symptoms

  • Eco mode not selectable
  • Eco indicator not working
  • Vehicle runs in normal mode

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–200
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

economy mode switchswitch wiringengine control module

Related codes

P05C7P05C8P05C9P0643

References: saabwisonline.com, law.cornell.edu.