OBD-II Code · Chassis
C1241
Brake Boost Vacuum Sensor
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Not for long
Driving on this one risks further damage. Get it to a shop rather than carrying on with it.
Indicative cost (USD)
$100–$800
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Brake booster vacuum sensor fault.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Hard brake pedal
- Warning
Likely causes
- Vacuum leakMost common
- Failed sensor
- Bad brake booster
Read the full diagnostic procedureC1241 is low voltage to the ABS module — the EBCM is seeing supply voltage below its operating threshold (typically under 10V key-on for most platfor…
C1241 is low voltage to the ABS module — the EBCM is seeing supply voltage below its operating threshold (typically under 10V key-on for most platforms, under 9V during cranking) and disabling ABS until voltage recovers.
Cheapest first by a wide margin
- load-test the battery before doing anything else.
- A battery that reads 12.4V at rest but drops below 10V under a 200-amp load is the cause of C1241 on probably 70% of cases; replacement is $120-$220 and the code never returns.
- If the battery passes load test, measure key-on voltage at the EBCM main power connector — it should be within 0.3V of battery voltage; anything more is a wiring/connector resistance problem (commonly a corroded eyelet at the main underhood junction or a chafed positive cable).
- Check alternator output: 13.8-14.8V at 2,000 rpm with a moderate load (headlights, blower on high).
- Watch live data for system voltage on the scan tool — should track within 0.2V of what you measure at the battery.
- The classic expensive misdiagnosis: replacing the alternator ($300-$600) when a $150 battery would have fixed it, because techs assume a charging-system fault without doing the 5-minute battery load test first.
- Same with replacing the EBCM ($800+) when the actual fault was a corroded battery terminal.
Vehicle-specific patterns2004-2012 GM full-size trucks/SUVs — C1241 sets within 2 weeks of a weak/dying battery; AC Delco group 78 replacement fixes it.
- 2004-2012GM full-size trucks/SUVs — C1241 sets within 2 weeks of a weak/dying battery; AC Delco group 78 replacement fixes it.
- 2005-2010Ford F-150 — corroded positive battery cable at the megafuse, replace cable assembly ($85).
- 2007-2013Jeep Wrangler JK — undersized factory battery struggles in cold weather, upgrade to group 65 deep-cycle.
- 2010-2015Chevy Equinox — C1241 after any jump-start event; battery often damaged by the jump and needs replacement.
Estimated repair$20 to $900.
Look up another code
C1241 — frequently asked
What does a C1241 code mean?
Brake booster vacuum sensor fault.
What causes a C1241 code?
Common causes: Vacuum leak; Failed sensor; Bad brake booster.
What are the symptoms of a C1241 code?
Typical symptoms: Hard brake pedal; Warning.
Is it safe to drive with a C1241 code?
Not for long. Driving on this one risks further damage. Get it to a shop rather than carrying on with it. Estimated repair: $100-$800.
How do I diagnose a C1241 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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