Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
ECM Input Code EI78 - Power Steering Pressure Switch Circuit: Notes
The power steering switch is normally closed and opens with high power steering pressure. During normal driving, the power steering switch receives 12 volts from the 10-amp ECS fuse over circuit No. 639B, and sends the 12-volt signal to ECM on circuit No. 495. When high power steering pressures occur, the switch opens and circuit No. 495 voltage is read by ECM as zero volts.
The ECM uses power steering input to extend the ISC motor when high power steering pressures occurs at low speeds, such as parking maneuvers.
- Input test EI78 must be performed with engine running.
- Status "STAYS HI" means that switch is not opening with high pressure or that circuit No. 495 is shorted to voltage.
- Status "STAYS LO" means that ECM never receives a 12-volt signal on circuit No. 495.
- Unplug and plug ECM connector and ensure it is latched properly.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.