1.0 | Code P1571 – Traction Control Torque Request Signal
Complete Technical Reference Guide: Diagnostics, Related Codes, Component Analysis & Repair Procedures
Technical Definition & System Architecture
2.1 System Architecture Overview
Diagnostic Trouble Code (DTC) P1571 – Traction Control Torque Request Signal represents a critical communication failure within the vehicle’s electronic stability control network. This code is specifically triggered when the Engine Control Module (ECM) fails to receive a valid torque reduction request signal from the Electronic Brake Control Module (EBCM) or Vehicle Stability Control (VSC) module during traction control events.
The torque request system operates on a Controller Area Network (CAN bus) architecture, typically using ISO 15765-4 (CAN 11-bit 500kbps) or ISO 14229 (UDS) protocols. When wheel slip is detected, the traction control module calculates required torque reduction (typically 10-80% of available torque) and transmits this request via dedicated CAN messages (message ID 0x0B5 for GM systems, 0x0AA for Bosch systems).
2.2 Signal Communication Protocol
The torque request signal consists of multiple data fields within the CAN message:
| Data Field | Byte Position | Value Range | Description | Units |
|---|---|---|---|---|
| Torque_Request | Bytes 0-1 | 0x0000-0xFFFF | Requested torque reduction percentage | % (0-100) |
| Request_Valid | Byte 2, Bit 0 | 0/1 | Signal validity flag | Boolean |
| Priority_Level | Byte 2, Bits 1-3 | 0-7 | Request priority (ABS vs TCS) | Level |
| Wheel_Slip_Status | Byte 3 | 0x00-0xFF | Individual wheel slip detection | Bitmask |
| Checksum | Byte 7 | 0x00-0xFF | Message integrity check | – |
Related Diagnostic Trouble Codes
3.1 Commonly Associated Codes
P1571 rarely occurs in isolation. The following DTCs frequently accompany or precede P1571, indicating broader system failures:
| DTC Code | Description | System | Severity | Relationship to P1571 |
|---|---|---|---|---|
| U0100 | Lost Communication with ECM/PCM | Network | High | Direct CAN bus failure affecting all ECM communication |
| U0121 | Lost Communication with ABS Control Module | Network | High | Specific module communication failure |
| C0569 | System Disabled – Traction Control | Chassis | Medium | Traction control system self-disabled due to internal fault |
| P2135 | Throttle/Pedal Position Sensor “A”/”B” Voltage Correlation | Powertrain | Medium | Faulty throttle position affects torque calculation |
| P1569 | TC Torque Reduction Signal Range/Performance | Powertrain | Medium | Signal present but out of expected range |
| U0401 | Invalid Data Received from ECM | Network | High | ECM sending corrupt data to other modules |
3.2 Vehicle-Specific Code Variations
Different manufacturers implement P1571 with additional subcodes or manufacturer-specific codes:
General Motors
P1571-00: Signal Missing
P1571-71: Invalid Serial Data
P1571-96: Actuator Stuck/Blocked
BMW
5E20: DSC: Torque Request Fault
5E21: DSC: Interface to DME Fault
5E22: DSC: CAN Timeout
Volkswagen/Audi
01314: Engine Control Module
01316: ABS Control Module
00473: Control Module for Elect. Parking Brake
Advanced Diagnostic Procedures
Step 1: Network Communication Verification
Begin with comprehensive network diagnostics using professional scan tools capable of CAN bus analysis:
- CAN Bus Voltage Test: Measure CAN High (Pin 6 – typically 2.6V) and CAN Low (Pin 14 – typically 2.4V) at OBD-II port with ignition ON
- Termination Resistance: Check for 60Ω resistance between CAN High and CAN Low (120Ω at each module)
- Module Communication Status: Verify all modules appear on network (ECM, TCM, EBCM, BCM)
- Live Message Capture: Monitor CAN bus for Torque_Request messages (ID 0x0B5 or manufacturer-specific)
Step 2: Signal Path & Wiring Analysis
Physical inspection and testing of the communication pathway:
- Wiring Inspection: Focus on ECM connectors C1 (GM: Pin 71), EBCM connectors, and intermediate junctions
- Pin Drag Test: Check for loose terminals in all related connectors (0.5N maximum insertion/removal force)
- Continuity Testing: Verify CAN High/Low continuity between modules (should be 0-5Ω)
- Shorts to Power/Ground: Test for short circuits to battery voltage or chassis ground
Step 3: Module Functional Testing
Isolate and test individual control modules:
- ECM Signal Generation Test: Command torque reduction via scan tool (if supported)
- EBCM Self-Test: Perform ABS/TC module actuator test and internal diagnostics
- Power & Ground Circuit Analysis: Verify clean power (≤0.5V drop) and ground (≤0.1Ω) to all modules
- Software Verification: Check for TSBs regarding calibration updates or reflash requirements
Critical Diagnostic Note
DO NOT replace the ECM as a first step. 78% of P1571 cases are resolved through wiring repairs, connector servicing, or software updates. Always perform complete network diagnostics before module replacement.
Component Failure Analysis & Specifications
5.1 Common Failure Points
| Component | Failure Rate | Typical Symptoms | Diagnostic Test | Repair Procedure |
|---|---|---|---|---|
| ECM Connector C1 | 32% | Intermittent code, corrosion at pins 70-73 | Pin drag test, visual inspection | Connector replacement, dielectric grease |
| CAN Bus Wiring (Under Carpet) | 28% | Moisture damage, rodent damage | Continuity test, insulation resistance | Wire repair with soldered splice |
| EBCM Power Supply | 18% | Multiple ABS/TCS codes | Voltage drop test (≤0.5V) | Fuse/relay replacement, clean grounds |
| Software Calibration | 15% | Code returns after clearing | Check TSBs, flash counter | Module reprogramming |
| Wheel Speed Sensors | 7% | Incorrect wheel speed data | AC voltage test (100mV-3.5V AC) | Sensor replacement, tone ring cleaning |
