Cadillac C121D: Improper Shutdown

Is your scanner showing Cadillac C121D?
No worries. We'll show you what it means and how to deal with it.

Presented by

Randy Worner

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Cadillac C121D: Improper Shutdown

OVERVIEW

Severity

High

DIY Difficulty Level

Intermediate

Repair Cost

$300-$400

Can I Still Drive?

Yes (Short-term only)

What Does The Cadillac C121D Code Mean?

A Key Off cycle was interrupted before completion, or power was removed from the module with the key in the ON position, vehicle moving and brake is applied.

Condition for setting the DTC:

Ignition ON. The ignition voltage is greater than 10 volts. The EBCM is initializing.

What Are The Symptoms Of The Cadillac C121D Code?

A lack of brake assist (Hard Pedal) after disconnecting the battery or after the 12v battery has run low on voltage
ABS and red brake lamp

What Are The Potential Causes Of The Cadillac C121D Code?

This may be caused by an improper 12v battery disconnect procedure.

How Can You Fix The Cadillac C121D Code?

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed:

1. Install the negative battery cable to the battery.
2. Rotate the lever lock clockwise until an audible click is heard in order to connect the negative battery cable to the battery.
3. Position the negative battery cable insulating cover over the negative terminal.
4. Start the vehicle without stepping on the brake pedal.
5. Shut the vehicle “Off” for one minute.
6. Restart vehicle and check brakes for proper operation.
7. Clear codes in the ECM and the EBCM.