P1674 – ABS/TCS Torque Request Signal: Complete Technical Diagnostic Manual
Comprehensive guide covering electrical specifications, network protocols, wiring diagrams, and step-by-step diagnostic procedures for professional technicians and advanced enthusiasts.
Technical Definition: P1674
OBD-II Code P1674 is a manufacturer-specific diagnostic trouble code that indicates a malfunction in the Torque Request Communication Circuit between the Anti-lock Braking System (ABS) Module and the Powertrain Control Module (PCM).
Technical Specification: This code is set when the PCM detects an invalid, missing, or implausible torque reduction request signal from the ABS/TCS module for a duration exceeding 2 seconds, or when the signal voltage remains outside the expected operating range of 0.5V to 4.5V on a 5V reference circuit.
Protocol: Typically transmitted via Class 2 Serial Data (GM vehicles), CAN bus (Controller Area Network), or ISO 9141-2 protocols depending on vehicle year and manufacturer.
1.0 System Operation & Signal Flow
1.1 Torque Request Signal Purpose
The torque request signal is a critical component of modern vehicle stability control systems. When wheel slip is detected by the ABS module (via wheel speed sensors), the system calculates the required torque reduction and sends a digital request to the PCM. This request can range from 0% (no reduction) to 100% (complete torque cut-off) and is typically transmitted at a frequency of 100-500 Hz.
1.2 Communication Protocol Details
2.0 Related Diagnostic Trouble Codes
P1674 rarely occurs in isolation. Understanding related codes is essential for accurate diagnosis.
2.1 Commonly Associated ABS/TCS Codes
3.0 Comprehensive Symptom Analysis
3.1 Primary Symptoms
Critical Safety System Warning
The illumination of the ABS, Traction Control, and Stability Control warning lights indicates complete or partial disablement of electronic stability systems. This represents a SEVERE safety concern requiring immediate attention.
4.0 Professional Diagnostic Procedure
4.1 Required Equipment
- Advanced OBD-II Scanner with ABS/TCS module access
- Digital Multimeter with Min/Max recording
- Oscilloscope (recommended for network analysis)
- Vehicle-specific wiring diagrams
- Breakout box for module connectors
- Terminal removal tools
4.2 Step-by-Step Diagnostic Flowchart
Diagnostic Algorithm:
5.0 Electrical Specifications & Wiring
5.1 ABS Module Connector Pinout (Typical GM)
Voltage: 2.5-3.5V
Circuit: 2500
Voltage: 1.5-2.5V
Circuit: 2501
Voltage: 12V Key ON
Fuse: ABS 10A
Voltage: 12V Constant
Fuse: 60A Maxi
Resistance: <0.5Ω to battery
Location: Left frame rail
Frequency: 7 Hz @ 1 mph
AC Voltage: 0.1-1.5V
5.2 Voltage Specifications Table
6.0 Vehicle-Specific Technical Data
6.1 General Motors (2007-2014 Models)
Common Vehicles: Chevrolet Silverado 1500, Tahoe, Suburban, GMC Sierra, Cadillac Escalade
TSB Reference: #PI-00123 (Updated ABS Module Calibration), #PI-00987 (Wheel Speed Sensor Connector Corrosion)
Module Location: Driver side frame rail, near master cylinder
Programming Required: YES – SPS programming via Tech2 or GDS2
6.2 Ford Motor Company (2009-2016 Models)
Common Vehicles: F-150, Expedition, Explorer
Network Type: MS-CAN (Medium Speed CAN)
Module Location: Passenger side kick panel
Special Note: Requires ABS module initialization after battery disconnect
7.0 Technical Frequently Asked Questions
The torque request signal is a digital message sent from the ABS module to the PCM containing a requested torque reduction percentage (0-100%) based on wheel slip calculations. The PCM then implements this request through throttle closure, ignition timing retardation, or fuel injection reduction to regain traction.
Yes. Modern transmissions use wheel speed data for shift calculations. Erratic wheel speed signals or missing torque requests can cause harsh shifting, delayed shifts, or torque converter clutch engagement issues. This is particularly common in 6L80/6L90 transmissions in GM trucks.
Using a digital multimeter, measure between CAN High and Ground: Should be 2.5-3.5V. CAN Low to Ground: 1.5-2.5V. CAN High to CAN Low: Should show a differential of 1.0V ± 0.4V. Any readings outside these ranges indicate network problems.
Connect oscilloscope leads to the sensor terminals. Rotate wheel at exactly 60 RPM (1 Hz). The waveform should be a clean sine wave with frequency proportional to speed (typically 7 Hz per mph). Amplitude should increase linearly with speed. Look for dropout, noise, or irregular patterns indicating sensor or tone ring damage.
Absolutely. Alternator ripple voltage exceeding 100mV AC can corrupt network communications. Test alternator output with an oscilloscope looking for AC ripple. More than 0.5V AC ripple at any RPM can cause intermittent P1674 codes, especially when electrical load is high.
Always diagnose in this order: 1) Power and ground faults, 2) Wheel speed sensor codes, 3) Network communication codes, 4) Module internal fault codes, 5) P1674 specifically. This follows the principle of diagnosing the cause before the symptom.
