When a 2017 Chevy Malibu with a 1.5L engine arrived with steering angle sensor issues after a rack and pinion replacement, it presented a challenging diagnostic puzzle. The initial repair shop had installed a used rack and pinion, performed an alignment, but couldn’t calibrate the steering angle sensor. This article details the diagnostic process, highlighting the importance of using new modules on GM Global A vehicles and the intricacies of Autel Calibrating Malibu Steering systems.
Understanding GM’s Global A Architecture and Module Programming
General Motors transitioned to the Global A architecture starting in 2010, completing the shift by 2014. This architecture requires using the GDS 2 scan tool and mandates new module installations, as swapping modules can damage both the original and replacement units. GM provides handy charts (link) to identify Global A vehicles based on scan tool compatibility. Our 2017 Malibu fell squarely into this category, necessitating a new rack and pinion assembly with a fresh power steering control module (PSCM).
Programming the PSCM with ACDelco TDS and SPS
After the new rack and pinion installation and alignment, we used a J2534 passthrough device by Drew Technologies, connected to a Dell E7470 laptop, to program the PSCM. We logged into the ACDelco Technical Delivery System (TDS) and launched SPS (Service Programming System), GM’s dedicated programming application. The programming process itself was successful.
Replace Figure 2 with actual image from original article if available
The Calibration Challenge: Steering Stop Limits and Sensor Characteristics
Post-programming, the PSCM requires calibration to learn steering stop limits and the characteristics of the steering torque sensor and rotational motor. This calibration is crucial for proper system function. Initially, an error during this stage led to the assumption of a programming failure. However, further investigation revealed the issue lay within the calibration setup, a process distinct from programming. The error message within SPS pointed towards a calibration problem.
Replace Figure 3 with actual image from original article if available
Diagnosing the Steering Angle Sensor Issue
Despite successful programming, the steering angle sensor remained at 0, regardless of steering input. Live data confirmed the torque sensor functioned correctly, but the angle sensor showed no activity. Research revealed that this Malibu model lacks a dedicated steering angle sensor. Instead, the PSCM calculates steering angle by comparing motor rotation data with input from the steering torque sensor.
Replace Figure 6 with actual image from original article if available
Replace Figure 7 with actual image from original article if available
Verifying Power, Ground, and Communication Circuits
We meticulously checked the PSCM’s power, ground, and CAN communication circuits. All proved to be in perfect working order, eliminating them as potential causes.
Replace Figure 8 with actual image from original article if available
The Root Cause: Improper Rack and Pinion Installation
The original rack and pinion replacement was prompted by a warning message and a fault code suggesting a faulty steering angle sensor. Testing the original rack revealed a different fault code, indicating an internal issue. After a second new rack installation by the client, the same calibration issue persisted. A thorough inspection uncovered a rubbing sound during sharp turns, indicating misalignment. The right front tire rubbed against the lower control arm at full right turn, and the steering wheel had uneven turns from center. Further inspection revealed a loosely secured intermediate steering shaft with an incorrect bolt and a camber kit on the left front strut, suggesting prior damage or improper repairs.
Resolution: Proper Rack Centering and Alignment
We centered the rack and pinion manually, ensuring equal turns from lock to lock. After securing the steering shaft with the correct bolt and performing a wheel alignment, the PSCM setup finally completed successfully. The root cause was multiple improper rack and pinion installations, leading to incorrect steering stop limits and hindering the calibration process. The PSCM, sensitive to these inconsistencies, prevented calibration until proper alignment was achieved. This case underscores the critical role of accurate installation procedures and highlights the diagnostic power of understanding system interactions and utilizing tools like Autel for calibrating Malibu steering systems.
