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DTC codes / C07xx · Brakes, steering and suspension / C0740

C0740Electric Power Steering Voltage Supply

C0740 indicates that the electric power steering (EPS) control module has detected an abnormal voltage supply condition, either too low or too high, on its power feed circuit. The module monitors the voltage at its main supply input and sets this code when the reading falls outside the manufacturer's specified operating range for a calibrated time, which can disable or reduce power assist.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • The power steering warning light or a red steering wheel icon illuminates on the dashboard.
  • Steering effort increases noticeably, especially at low speeds or during parking maneuvers.
  • The power assist may cut in and out intermittently, causing a jerky or inconsistent steering feel.
  • A chime or message such as 'Power Steering Assist Fault' appears in the driver information center.
  • In some vehicles the system enters a fail-safe mode that limits assist to a fixed reduced level.
  • Often no symptoms besides the warning light, with steering feel unchanged during normal driving.

Common causes, most likely first

  1. A weak or failing 12-volt battery that cannot maintain stable voltage under load.
  2. Corroded, loose, or damaged battery terminal connections and ground straps.
  3. A faulty alternator or charging system that allows supply voltage to sag or spike.
  4. Damaged or chafed wiring in the EPS power supply circuit, including blown fuses or fusible links.
  5. High resistance at the EPS module power connector pins due to corrosion or poor pin tension.
  6. An internal fault in the EPS control module causing it to misread its own supply voltage.
  7. Voltage drop from aftermarket accessories or improper jump-starting that stresses the EPS supply.

How to diagnose and fix it

  1. Perform a battery load test and check the charging system output with a voltmeter; replace the battery or repair the charging system if voltage is out of specification.
  2. Inspect and clean battery terminals, ground connections, and the EPS module ground point; tighten any loose fasteners.
  3. Check all fuses and fusible links that feed the EPS module, and verify voltage at the module power connector with the key on and engine running.
  4. Perform a voltage drop test on the positive and ground sides of the EPS supply circuit under load to locate excessive resistance.
  5. Inspect the wiring harness for chafing, corrosion, or loose pins at the EPS module connector and repair as needed.
  6. Clear the code and test-drive the vehicle; if the code returns after supply voltage is confirmed good, suspect an internal EPS module fault.
  7. Follow the manufacturer's diagnostic flow chart for C0740, which may include reprogramming or replacing the EPS control module as a last step.

Voltage supply faults that mimic module failure

  • A marginal battery that still starts the engine can cause C0740 because the EPS module draws high current during parking maneuvers, pulling supply voltage below the threshold.
  • Corroded ground connections on the chassis or engine block are a frequent hidden cause, since the EPS module references its voltage to ground and a poor ground skews the reading.
  • Jump-starting another vehicle or being jump-started incorrectly can spike the EPS supply and set this code even though no component has failed.
  • Aftermarket electrical accessories tapped into the EPS circuit can create voltage drops that trigger C0740 only when those accessories are in use.
  • The code does not always mean the EPS module is bad; many modules are replaced unnecessarily when the real fault is a weak battery or a corroded cable.

Can I keep driving with C0740?

You can usually drive the vehicle, but expect heavier steering and reduced assist, which makes low-speed maneuvers more difficult. Avoid high-speed evasive maneuvers and have the charging system and battery checked promptly, since a voltage supply fault can worsen and lead to a sudden loss of assist.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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