What Does C1781 Mean?
The chassis control module is not receiving a valid engine coolant temperature (ECT) signal. This data is typically shared over the CAN bus from the PCM and is used by the ABS/stability control system to adjust braking strategies based on engine temperature (e.g., cold start brake boost, traction control sensitivity). The driver may see a stability control warning light and the system may use a default temperature value.
Common Causes
35%
CAN bus communication fault between PCM and chassis module
25%
PCM not broadcasting coolant temperature data due to its own ECT sensor fault
20%
Chassis module software calibration issue or module needing reprogramming
15%
Mismatched modules after replacement without proper configuration
5%
Intermittent power or ground supply to chassis module causing data reception gaps
Diagnostic Steps
1
Check for related PCM codes — if P0115, P0116, P0117, or P0118 are also stored, the root cause is the engine coolant temperature sensor or its circuit rather than the chassis module.
2
Monitor the ECT PID from both the PCM and the chassis module simultaneously in live data — if the PCM shows a valid reading but the chassis module does not, the issue is CAN communication or the chassis module itself.
3
Inspect CAN bus wiring between the PCM and chassis module for damage, focusing on connector pins at both modules and any intermediate splice packs.
4
Verify chassis module power and ground supplies with a multimeter: battery voltage at power pins and <0.1V drop on ground pins with the key on.
5
If modules were recently replaced or the battery was disconnected, perform a module configuration/setup procedure using the scan tool to re-establish proper CAN message parameters.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The chassis control module is not receiving a valid engine coolant temperature (ECT) signal. This data is typically shared over the CAN bus from the PCM and is used by the ABS/stability control system to adjust braking strategies based on engine temperature (e.g., cold start brake boost, traction co...
The most common cause of C1781 (Engine Coolant Temperature Signal Missing/Fault) is: CAN bus communication fault between PCM and chassis module
Typical repair costs for C1781 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to continue driving. The chassis module will use a default temperature value, which may slightly affect cold-start traction control sensitivity. No significant safety risk for normal driving conditions. Diagnose at your convenience.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1781 to identify the root cause.
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Quick Info
Category
Chassis
System
Chassis Electronics / ABS-Traction Control
Difficulty
Type
Manufacturer
Recommended Tools
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