Drivability Diagnosis

Systematic diagnosis of drivability issues on a 2023 Chevrolet Bolt EUV electric vehicle, including electrical system verification, drive unit inspection, and diagnostic scan tool analysis.

Warnings

Tools required

Parts

• 12V battery (if failed) × 1 — Use OEM specification
• High voltage connector seals (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake firmly
2. Ensure vehicle is in PARK and ignition is OFF
3. Verify customer complaint by obtaining detailed description of symptoms including when they occur (acceleration, deceleration, temperature conditions)
4. Check for any active recall campaigns or TSBs related to drivability concerns for this model year
5. Ensure diagnostic scan tool has latest GM software version for 2023 Bolt EUV
6. Put on insulated high-voltage gloves if inspection of HV components will be required

Procedure

1. 1

   Perform initial visual inspection
   Open hood and inspect for obvious issues: damaged wiring harnesses, loose connectors, fluid leaks (coolant or brake fluid), or physical damage to drive unit components. Check that all high-voltage connectors (orange) are fully seated and locking tabs engaged. Inspect 12V battery terminals for corrosion or looseness.
2. 2

   Connect scan tool and retrieve fault codes
   Connect GM MDI 2 or compatible J2534 scan tool to OBD-II port under driver's side dash. Turn ignition to ON position without pressing brake pedal (do not enter READY mode). Retrieve all diagnostic trouble codes (DTCs) from all modules, paying particular attention to Propulsion Power Inverter Module, Battery Energy Control Module, Drive Motor Control Module, and Electronic Brake Control Module. Record all codes, freeze frame data, and failure counters.
3. 3

   Test 12V battery system
   Using digital multimeter, measure 12V battery voltage with vehicle OFF (should be 12.4-12.8V). Turn ignition ON and verify voltage remains above 12.0V. If voltage is low, perform battery load test. A weak 12V battery can cause erratic behavior in electric vehicles including communication errors, reduced power, and false fault codes. Replace battery if it fails load test.
4. 4

   Analyze live data parameters
   With scan tool, monitor live data while vehicle is in READY mode (press brake and push start button). Key parameters to observe: High Voltage Battery State of Charge (SOC), High Voltage Battery Voltage (should be 300-400V depending on SOC), Drive Motor Temperature, Inverter Temperature, Coolant Temperature, Accelerator Pedal Position, Motor Torque Command vs Actual, and Regenerative Braking Status. Note any parameters that are out of expected range or not responding properly to inputs.
5. 5

   Perform stationary test drive simulation
   With vehicle safely elevated on lift (if available) or on level ground in PARK, observe scan tool data while simulating conditions. If elevated with wheels free, shift to DRIVE and gently apply accelerator while monitoring motor torque, voltage, and current parameters. Listen for unusual noises from drive unit. If on ground in PARK, monitor accelerator pedal sensor data for smooth linear response when pedal is pressed.
6. 6

   Inspect high-voltage connections and cables
   Turn ignition OFF and disconnect 12V battery negative terminal. Wait 5 minutes for high-voltage system to discharge. Wearing insulated high-voltage gloves, visually inspect all orange high-voltage cables for damage, chafing, or signs of arcing. Check HV battery connections, drive unit connections, and inverter connections for proper seating, corrosion, or damage to seals. Do not disconnect HV connectors unless specifically required by diagnostic procedures.
7. 7

   Check drive unit and mounting points
   Inspect electric drive unit for leaks (reduction gear oil appears as dark oil near seals), unusual residue, or physical damage. Check drive unit mounting bolts for proper torque and condition. Examine CV axles for tears in boots or excessive play. Rock axles by hand to check for worn joints that could cause clicking or vibration during acceleration.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
8. 8

   Verify propulsion cooling system
   Check coolant level in propulsion cooling system reservoir (separate from HVAC system). Coolant should be between MIN and MAX marks and be orange DEX-COOL. Low coolant can cause drive unit or inverter overheating leading to reduced power. Inspect hoses and connections for leaks. Verify coolant pump operation using scan tool active tests if available.
9. 9

   Test regenerative braking system
   Reconnect 12V battery if disconnected. Start vehicle to READY mode. In a safe location, test regenerative braking by releasing accelerator at various speeds and observing deceleration feel and paddle shifter response (if equipped with One-Pedal Driving). Monitor scan tool for regenerative braking torque values and battery charging current. Reduced or absent regenerative braking can indicate drive unit, inverter, or battery control issues.
10. 10

    Perform road test with scan tool data logging
    If initial diagnostics have not revealed fault, perform controlled road test while data logging with scan tool. Attempt to replicate customer complaint conditions. Monitor all propulsion system parameters during acceleration, steady cruise, deceleration, and regenerative braking. Note exact conditions when any abnormal behavior occurs and correlate with data log.
11. 11

    Analyze diagnostic results and determine root cause
    Review all collected data: fault codes, freeze frames, live data anomalies, physical inspection findings, and road test observations. Cross-reference DTCs with GM service information for specific diagnostic procedures. Common drivability causes include: failed drive motor position sensors, inverter faults, high-voltage battery cell imbalances, 12V electrical issues, software calibration problems, or mechanical drive unit damage. Formulate specific diagnosis and repair plan.

Reassembly

1. Ensure all high-voltage connectors are fully seated with locking tabs engaged if any were inspected
2. Reconnect 12V battery negative terminal if it was disconnected
3. Verify all inspection covers and panels are reinstalled securely
4. Clear any non-permanent diagnostic codes if diagnosis did not reveal faults

Verification

• Perform final scan for DTCs - verify no new codes have set during diagnostic process
• Start vehicle to READY mode and verify all warning lights extinguish normally
• Test drive vehicle and verify drivability concern is identified or, if repaired, verify normal operation
• Confirm regenerative braking functions properly and smoothly
• Verify propulsion system operates quietly without unusual noises or vibrations
• Document all findings, test results, and recommended repairs for customer review

More procedures for this vehicle