How severe is fault code C1240?

Serious — Stop or limit driving

OBD Code C1240: ABS Hydraulic Pressure Differential Switch Input Short Circuit To Battery

Q: What are the symptoms of fault code C1240?

ABS warning light illuminated on dashboard, Loss of ABS braking functionality, Brake pedal may feel different or harder than normal

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What This Actually Means

In plain language — no jargon

The ABS system's hydraulic pressure sensor is receiving a constant high voltage signal (shorted to battery power) instead of varying normally. Think of it like a light switch stuck in the 'on' position—the ECU can't read real pressure changes.

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Symptoms You May Notice

3 known symptoms for this code

ABS warning light illuminated on dashboard

Loss of ABS braking functionality

Brake pedal may feel different or harder than normal

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Embedded Systems Insight

What the ECU/ECM is actually computing

The ECU monitors the hydraulic pressure differential switch signal voltage to detect pressure changes during ABS events. The sensor normally provides a variable analog voltage between 0–5V corresponding to pressure states. A short-to-battery condition locks the signal at maximum voltage, preventing the ECU from detecting actual pressure conditions.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Sensor signal voltage	0.5–4.5V (variable with pressure)	Continuously 5V (shorted to battery)
Pressure detection	Sensor responds to pressure changes	No voltage variation detected

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Wiring harness connector at ABS sensor

Inspect connector pins for corrosion, moisture, or bent terminals; clean or reseat firmly.

2

Hydraulic pressure differential switch sensor

Replace the sensor if connector inspection reveals no issues; typically 2-3 bolts to remove.

3

ABS wiring harness

Check for damaged insulation or pinched wires along the sensor circuit; repair or replace compromised sections.