C1236

DTC C1236: Low System Supply Voltage (Part 1 Of 2):

DTC C1236: Low System Supply Voltage (Part 2 Of 2):

DTC C1236 Schematic:

Circuit Description
This DTC is used to monitor the voltage level available to the Electronic Brake Control Module (EBCM). If the voltage drops below specific levels at specific times, full performance of the ABS system cannot be guaranteed. During an ABS event, there are several current requirements that will cause battery voltage to drop. Because of this, voltage is monitored prior to an ABS event and also during an ABS event operation when voltage may drop significantly.

Conditions for Setting the DTC
This DTC will set when the following conditions are met:
^ This DTC can only be set if the vehicle's speed is greater than 5 km/h (3 mph).
^ Both the switched battery (CKT 850) and switched ignition (CKT 350A/B/C) voltages are less than 11.5 volts during non-ABS event, or less than 9.3 volts during an ABS event.
^ Switched battery (CKT 850) voltage falls below 8.52 volts during motor rehome.

Action Taken When the DTC Sets
A malfunction DTC is stored, ABS is disabled, and the amber ABS indicator lamp is turned ON. The red BRAKE warning lamp is turned ON if the rear piston in the motor pack is not expected to be in the home position.

Conditions for Clearing the DTC
^ Conditions for the malfunction are no longer
present and the Tech 2 scan tool Clear DTC Information function is used.
^ One hundred drive cycles have passed with no malfunctions detected.

Diagnostic Aids
The following list contains items that need to be inspected when diagnosing this system:
^ Vehicle charging system is not operating properly (low alternator output, faulty battery).
^ High resistance in CKTs 350A/B/C/D, 850 and 150A/B.
^ Poor G103.
An intermittent malfunction is most likely caused by a poor connection, rubbed through wire insulation or a wire that is broken inside the insulation.

The frequency of the malfunction can be checked by using the Enhanced Diagnostic function of the Tech 2 scan tool, as described in Enhanced Diagnostics. Inspect the following harness connectors for backed out terminals, improper mating, broken lock, improperly formed or damaged terminals and for poor terminal-to-wire connection before component replacement
^ EBCM connectors C1 and C2.
^ ABS relay harness connector terminals.



Test Description
The numbers below refer to step numbers on the diagnostic table.
2. Checks the vehicle charging system for good condition.
3. Performs voltage load test through scan tool command and checks for excessive voltage drop in CKT 850.
4. Checks for excessive voltage drop in CKT 350A/B/C/D.
5. Checks if DTC resets after two drive cycles.
6. Checks for high resistance in CKT 850.
7. Checks for high resistance in CKT 1446A/B.
8. Checks for high resistance across ABS relay contacts (when closed).
9. Checks for high resistance in CKT 1Y03.
15. Determines whether condition is a result of poor terminal contact(s) and not due to a faulty EBCM.