Mobile App Diagnosis of CAR FAILURES FOR NON TECHNICAL PERSONS



A Field Guide to Three Common, Serious Car Failures—With an OBD-II Playbook for Android/iOS App

Executive summary. You’re seeing three distinct problems:

  1. Charging/Electrical failure → battery light appears, throttle stops responding, engine stalls.
  2. Cooling failure → temp climbs quickly to ~90 °C and you’ve observed boiling in the coolant reservoir.
  3. Automatic-transmission harsh engagement → after driving for a while, you get a boom/clunk when selecting or changing gears, plus a gearbox warning lamp.

All three are diagnosable with a structured checklist and the right OBD-II data. Below is a comprehensive, publish-ready breakdown: how each system works, why these symptoms happen, what to test, what to fix, and how an OBD diagnostic analysis tool (like the app you’re building) can detect and prevent them.

1) Charging System Failure (Battery Light → No Throttle → Stall)

What’s happening

  • The alternator should maintain system voltage at 13.8–14.5 V while the engine runs.
  • If the alternator, belt, or wiring fails, voltage collapses → ECU, throttle body, fuel pump, and transmission control lose power → battery lamp lights up, the accelerator stops responding, and the engine stalls once the battery drains.

Fast triage

  • Visual: Inspect serpentine belt and tensioner.
  • Terminal check: Clean and tighten battery posts.
  • Multimeter (engine running):
    • 13.8–14.5 V = healthy.
    • < 13.2 V = charging fault.

    • 15.0 V = regulator failure.

  • Ripple test: > 0.4 V AC indicates alternator diode failure.

OBD-II signals & DTCs

  • PIDs: Control Module Voltage, Engine RPM, APP/TPS.
  • Codes: P0560 (System Voltage), P0562 (Low Voltage), P0563 (High).

Fixes

  • Replace alternator or regulator, service belt/tensioner, repair grounds, replace weak battery.

2) Cooling System Failure (Fast Rise to 90 °C, Reservoir Boiling)

90 °C is normal, but boiling means coolant flow or pressure loss.

Root causes

  • Flow: stuck thermostat, bad water pump, clogged radiator, airlock.
  • Cooling: radiator fan not cycling.
  • Pressure: weak cap.
  • Combustion leak: head gasket or cracked head.

Safe tests

  • Cold: Set coolant to correct level, inspect cap.
  • Warm-up: If heater stays cold while gauge rises → flow issue.
  • Fan check: Fans should run with A/C on and at temp.
  • Hose temps: Upper/lower hose difference reveals radiator function.
  • Block test (shop): Detects combustion gases in coolant.

OBD-II signals & DTCs

  • PIDs: Coolant Temp (ECT), Fan Command %, Vehicle Speed.
  • Codes: P0128 (thermostat), P0217 (overheat), P0480/81 (fan control).

Fixes

  • Replace thermostat, fan/relay, water pump, radiator cap.
  • Flush/bleed system.
  • If head-gasket confirmed → repair urgently.

3) Automatic-Transmission “Boom/Clunk” After Warm-Up

Why after a while

  • As ATF heats, thin/old/low fluid loses pressure → harsh shifts.
  • Soft mounts amplify the impact.
  • Faulty solenoids, sensors, or valve body can worsen the problem.

First checks

  • ATF level/condition: correct procedure; fluid should be red/pink, not burnt.
  • Mounts: Inspect for cracks/sagging.
  • Driveline slack: Check CV joints/U-joints.

OBD-II signals & DTCs

  • PIDs: ATF Temp, Gear Commanded vs Actual, TCC Slip, Line Pressure.
  • Codes: P0700 (TCM request), P0730 (gear ratio), P0715 (input sensor), P0741 (torque converter clutch), P0776 (pressure solenoid).

Fixes

  • Correct ATF level/spec, replace fluid & filter, service mounts, repair solenoids/valve body.

Interactions Between Failures

  • Low voltage can trigger transmission faults.
  • Overheating accelerates ATF breakdown.
  • Always fix charging and cooling first, then transmission.

Diagnostic Workflow

  1. Safety: Stop for overheating; measure voltage if battery lamp on.
  2. Charging: Check belt, posts, voltage, ripple.
  3. Cooling: Inspect coolant, heater, fans, hoses.
  4. Transmission: Verify ATF, scan TCM, log shifts.
  5. Re-test after repair with drive cycle.

The Role of an OBD-II Diagnostic App

PID watchlist

  • Electrical: Voltage, RPM.
  • Cooling: ECT, Fan State.
  • Transmission: ATF Temp, Gear Actual vs Commanded.

Derived metrics

  • Charging health: Voltage stability + ripple check.
  • Cooling stress: Coolant rise rate + fan response.
  • Shift harshness: ATF temp + gear mismatch.

UX recommendations

  • Color-coded severity levels.
  • Plain-language cards (“Voltage low: check alternator”).
  • Trend charts (voltage vs RPM, ECT vs time, ATF vs gear).
  • Mechanic Pack: 15 min logs + freeze frames.

Quick Checklists

Charging

  • [ ] Terminals clean/tight
  • [ ] Belt/tensioner OK
  • [ ] 13.8–14.5 V at idle
  • [ ] Ripple < 0.4 V
  • [ ] No charging DTCs

Cooling

  • [ ] Correct coolant/cap
  • [ ] Heater hot, fan cycles
  • [ ] ECT stable < 100 °C
  • [ ] No boiling/bubbling
  • [ ] No cooling DTCs

Transmission

  • [ ] ATF correct level/spec
  • [ ] Fluid clean
  • [ ] Mounts intact
  • [ ] ATF < 110 °C
  • [ ] No shift DTCs

Cost & Risk

  • Charging: Belt (low), alternator (mid). Risk: stall, module damage.
  • Cooling: Thermostat/fan (low-mid), pump/head gasket (mid-high). Risk: engine failure.
  • Transmission: ATF service (low), valve body/rebuild (mid-high). Risk: drivability loss.

Conclusion

The three failures—charging, cooling, and transmission—are interlinked but diagnosable. With structured OBD-II data, your app can move drivers from panic to clarity: detect, explain, and prevent breakdowns. By blending live signals, mechanical guidance, and predictive metrics, your platform can become more than a code reader—it becomes a driver’s safety net.

A diagnosis of one local car owner, Audi A3 Auto/Manual Transmission. 


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