c 1780
Thread Starter
Heel & Toe
Joined: Jul 2006
Posts: 20
Likes: 6
c 1780
I have a '98 C5 that is showing C 1780. Loss of steering position signal. I would like to trace the problem but I don't know where or what to look for. Is it a sensor or something similar? If so where would it be?
Thanks a lot.
Jack.
Thanks a lot.
Jack.
Safety Car
Joined: Jan 2001
Posts: 4,386
Likes: 689
From: Boise ID
A little info from the 98 service manual:
DTC C1780 Loss of Steering Position Signal
Circuit Description
The ESC module receives a steering position PWM signal from the Electronic Brake/Traction Control Module (EBTCM) on CKT 914. The ESC module uses this signal in order to determine the shock absorber control levels and will command a more firm setting if the vehicle is in a turn. The ESC module monitors the steering position circuit and can determine if a valid signal is sent from the EBTCM.
Conditions for Setting the DTC
The ESC module does not detect a valid steering position PWM signal from the EBTCM.
The condition must be detected for 5 seconds in 4 consecutive ignition cycles.
Action Taken When the DTC Sets
Stores a DTC C1780 in the ESC memory.
Ignores the steering position PWM input.
Will continue to control the shock absorbers using the lateral acceleration data sent from the EBTCM on the serial data line.
Sends a message to the IPC to display the SERVICE RIDE CONTROL message.
Conditions for Clearing the DTC
The ESC module detects a valid steering position PWM signal from the EBTCM.
A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
The IPC clearing DTCs feature.
Using a scan tool.
Diagnostic Aids
The following conditions may cause an intermittent malfunction:
An intermittent open or short (to ground or to voltage) on the steering position sensor CKT 914.
Intermittent operation of the EBTCM. Refer to ABS Diagnostic System Check .
If the ESC module does not receive a valid steering position PWM signal from the EBTCM, the RTD system will still function, but will ignore the steering position PWM signal. The RTD system uses lateral acceleration data sent from the EBTCM on the serial data line in order to substitute for a loss of the steering position PWM signal.
The ESC module uses an ignition cycle counter diagnostic approach to set this DTC. This requires the ESC module to detect the malfunction 4 times before setting the DTC. To disable this feature, use a scan tool to clear all DTCs before preforming diagnostic procedures.
An intermittent open or short (to ground or to voltage) on the steering position PWM circuit may cause a random firm/soft ride condition.
If the DTC is a history DTC, the problem may be intermittent. Using a scan tool, monitor the steering position sensor circuit while moving the related wiring and connectors. This can often cause the malfunction to appear.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
This step checks if any ABS/TCS DTCs are present. The EBTCM provides the ESC module with steering position data, therefore all ABS/TCS DTCs that are associated with the steering position sensor must be diagnosed and corrected before attempting to diagnose a DTC C1780.
This step checks if the ESC module is able to receive a steering position PWM signal from the EBTCM.
This step checks for opens or shorts (to ground or to voltage) on the steering position signal CKT 914.
This step checks for an intermittent malfunction and requests a thorough inspection of the related steering position sensor circuit wiring and connectors.
DTC C1780 Loss of Steering Position Signal
Circuit Description
The ESC module receives a steering position PWM signal from the Electronic Brake/Traction Control Module (EBTCM) on CKT 914. The ESC module uses this signal in order to determine the shock absorber control levels and will command a more firm setting if the vehicle is in a turn. The ESC module monitors the steering position circuit and can determine if a valid signal is sent from the EBTCM.
Conditions for Setting the DTC
The ESC module does not detect a valid steering position PWM signal from the EBTCM.
The condition must be detected for 5 seconds in 4 consecutive ignition cycles.
Action Taken When the DTC Sets
Stores a DTC C1780 in the ESC memory.
Ignores the steering position PWM input.
Will continue to control the shock absorbers using the lateral acceleration data sent from the EBTCM on the serial data line.
Sends a message to the IPC to display the SERVICE RIDE CONTROL message.
Conditions for Clearing the DTC
The ESC module detects a valid steering position PWM signal from the EBTCM.
A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
The IPC clearing DTCs feature.
Using a scan tool.
Diagnostic Aids
The following conditions may cause an intermittent malfunction:
An intermittent open or short (to ground or to voltage) on the steering position sensor CKT 914.
Intermittent operation of the EBTCM. Refer to ABS Diagnostic System Check .
If the ESC module does not receive a valid steering position PWM signal from the EBTCM, the RTD system will still function, but will ignore the steering position PWM signal. The RTD system uses lateral acceleration data sent from the EBTCM on the serial data line in order to substitute for a loss of the steering position PWM signal.
The ESC module uses an ignition cycle counter diagnostic approach to set this DTC. This requires the ESC module to detect the malfunction 4 times before setting the DTC. To disable this feature, use a scan tool to clear all DTCs before preforming diagnostic procedures.
An intermittent open or short (to ground or to voltage) on the steering position PWM circuit may cause a random firm/soft ride condition.
If the DTC is a history DTC, the problem may be intermittent. Using a scan tool, monitor the steering position sensor circuit while moving the related wiring and connectors. This can often cause the malfunction to appear.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
This step checks if any ABS/TCS DTCs are present. The EBTCM provides the ESC module with steering position data, therefore all ABS/TCS DTCs that are associated with the steering position sensor must be diagnosed and corrected before attempting to diagnose a DTC C1780.
This step checks if the ESC module is able to receive a steering position PWM signal from the EBTCM.
This step checks for opens or shorts (to ground or to voltage) on the steering position signal CKT 914.
This step checks for an intermittent malfunction and requests a thorough inspection of the related steering position sensor circuit wiring and connectors.
