Jeep Fault Code
Free · no signup12
No driveability symptoms; Usually appears after battery work.
System
Not specified
Symptom
No driveability symptoms; Usually appears after battery work.
Diagnosis & fix steps
Battery Disconnect.
LOGIC: The PCM has lost constant 12V power within the last 50 key-on cycles.
ACTION: 1. Ensure battery terminals are tight and free of corrosion.
2. Verify the "Memory Power" fuse is not blown.
FIX: No repair needed if battery was recently disconnected; otherwise, check for loose battery cables.
Red Seal field insights
Code 12 is almost always present on older Jeeps. It’s a "history" code. If you haven't disconnected the battery recently and this keeps appearing, check the main ground strap at the engine block.
Same code keeps coming back?
That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.
Read before you touch anything
- This is general reference information, not a repair manual. It is for trained, qualified technicians.
- Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
- Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
- You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
- Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.
Track this across your whole fleet
This code is free to read. AM Fleet Integrity lets your team log fault codes against assets, plus the full fault-code library, QR operator reporting, PM scheduling and predictive alerts. Start free — no credit card required.
Start your free trialRelated Jeep fault codes
- 14Rough idle; Engine "running rich" (smell of unburned gas); Poor throttle response.
- 11Engine cranks but won't start; Sudden stalling when hitting bumps; No spark.
- 21Poor fuel economy; High idle; Engine stays in "Open Loop" mode.
- 24High idle; Transmission shifting issues (XJ Auto); Engine won't return to idle quickly.
- 27Misfire under load; Engine "stumbling" at highway speeds.
- 33No driveability symptoms unless A/C is in use.
- 42Engine won't start or dies immediately; No fuel pump prime sound.
- 51Lean misfire; Hissing sound; Hesitation on acceleration.
- 55No symptoms.
- B1239Air Trapped at Floor Vents