Quick Answer
Intermittent electrical faults require extended data logging and systematic elimination — not the 30-minute scan-and-guess approach that most garages use. Here's how proper diagnosis capture
Intermittent electrical faults require extended data logging and systematic elimination — not the 30-minute scan-and-guess approach that most garages use. Here's how proper diagnosis captures faults that only appear under specific conditions.
"It did it again yesterday. Three times on the highway. But when I brought it to the garage, they drove it for 20 minutes and said they couldn't find anything wrong."
If you've ever said something like this, you've met the most frustrating category of vehicle failure: the intermittent fault. A problem that exists — you feel it, see it, hear it — but refuses to appear when a technician is looking.
This isn't a ghost. It's physics. And solving it requires an approach that most garages simply don't use.
An intermittent fault is a failure that occurs under specific conditions — conditions that may not be present during a standard garage inspection.
What makes them hard:
What makes them solvable: Extended data logging. Instead of trying to catch the fault in real-time during a short test drive, we record sensor data continuously until the fault occurs naturally. Then we analyze exactly what happened, when, and why.
Why this fails:
Problem 1: Codes may not be stored. Not all faults generate codes. Some intermittent conditions occur too briefly to trigger the ECU's fault recording threshold. A 200-millisecond voltage dropout may cause the customer to feel a momentary power loss but not register as a stored fault code.
Problem 2: Short drives don't reproduce complex conditions. If a fault requires 45 minutes of highway driving at 120 km/h in 45°C heat to manifest, a 20-minute drive around the industrial area won't find it.
Problem 3: "No fault found" doesn't mean "no fault exists." It means the diagnostic method was insufficient to capture the fault. The customer knows the problem is real. Telling them it doesn't exist destroys trust.
Instead of trying to witness the fault in person, we let the car record it for us.
How we set up extended monitoring:
What we're recording:
| Data Type | Parameters | Why It Matters | |-----------|-----------|----------------| | Engine sensors | RPM, load, timing, fuel trim, throttle | Identifies performance anomalies | | Electrical | Battery voltage, alternator output, current draw | Catches voltage dropouts and spikes | | Temperature | Coolant, intake, exhaust, ambient | Reveals thermal-triggered faults | | Communication | CAN bus messages between modules | Identifies intermittent communication failures | | Driver inputs | Speed, brake, steering, throttle position | Correlates driver actions with fault timing |
The key difference: Instead of looking for the fault at one moment in time, we have a complete recording of everything that happened before, during, and after the fault occurred. This is the difference between a snapshot and a surveillance camera.
After thousands of intermittent fault diagnoses across luxury vehicles in Dubai, these are the root causes we find most often:
What it is: Electrical connectors throughout the vehicle develop internal corrosion from heat cycling and moisture exposure. Corroded pins have variable resistance — sometimes they conduct normally, sometimes they don't.
How it manifests: Random warning lights, occasional sensor reading errors, features that work intermittently (e.g., seat heater works sometimes, doesn't others).
Why Dubai is worse: Daily temperature swings of 30°C cause condensation inside connector housings. UV radiation degrades connector seals faster. Dust and sand infiltrate through degraded seals.
Diagnosis method: Signal quality analysis during data logging shows resistance spikes on affected circuits. Physical inspection reveals corroded pins invisible to visual checks without disassembly.
What it is: Wiring looms rub against body panels, brackets, or each other during normal vehicle operation. Over time, insulation wears through, exposing copper. The exposed wire makes intermittent contact with ground (metal body) when the vehicle moves in specific ways.
How it manifests: Faults that appear on rough roads, during turns, or over bumps. The fault disappears on smooth roads because the chafed wire isn't touching ground.
Why Dubai is worse: Dubai's road construction creates constant vibration. Speed bumps are everywhere. Fine sand gets between harness and body, accelerating abrasion.
Diagnosis method: Data logging shows fault correlation with road surface and vehicle movement. Physical inspection along the harness path (guided by data) reveals the chafe point.
What it is: Certain electronic components (capacitors, resistors, semiconductors) change behavior at extreme temperatures. A component that works perfectly at 30°C may malfunction at 60°C.
How it manifests: Faults that only appear after the car has been driven for 30+ minutes in hot weather. The component heats to its failure threshold, causes a fault, then recovers when it cools slightly.
Why Dubai is worse: Engine bay temperatures reach 65-75°C in summer traffic. Electronic modules mounted in the engine bay experience sustained temperatures that would never occur in temperate climates.
Diagnosis method: Temperature data logging correlates fault occurrence with specific module temperatures. Thermal imaging during fault condition identifies the overheating component.
What it is: ECU software has edge cases — combinations of inputs that the engineers didn't fully account for. When specific conditions align, the software enters an unexpected state.
How it manifests: Faults with very specific trigger patterns (e.g., only at exactly 2,200 RPM under half-throttle with A/C on). Consistent pattern once identified, but seemingly random before analysis.
Why Dubai is worse: Manufacturers typically calibrate and test in European or Asian conditions. Dubai's extreme temperature range, elevation (near sea level), fuel composition, and driving patterns create operating conditions outside the original calibration envelope.
Diagnosis method: Data logging reveals the exact input combination that triggers the fault. Cross-referencing with manufacturer technical bulletins often identifies a known software update that addresses the condition.
What it is: Every electronic circuit in your vehicle relies on clean ground connections — metal-to-metal contact points where wiring connects to the vehicle body. Over time, these points corrode, creating variable resistance in the ground path.
How it manifests: Multiple seemingly unrelated faults that come and go. Lights flickering, sensors reading incorrectly, modules resetting randomly. Because many circuits share ground points, one bad ground can cause symptoms across different systems.
Why Dubai is worse: Salt air from the Gulf, fine sand abrading surface treatments, and thermal expansion/contraction all accelerate ground point corrosion.
Diagnosis method: Voltage drop testing across ground circuits during data logging shows excessive resistance at specific ground points. Physical inspection and cleaning of ground points resolves the issue.
Vehicle: 2019 Mercedes-Benz S450 Symptom: Random COMAND (infotainment) system restart, occurring 2-3 times per week
What three previous shops found: "No fault stored. Could not reproduce."
What extended monitoring revealed:
We configured XENTRY (Mercedes factory diagnostic) for continuous CAN bus logging and returned the car to the owner. Over 5 days, the system recorded three restart events.
Data analysis showed:
Root cause path:
The fix: Cleaned and treated COMAND module power connector, applied dielectric grease, verified pin tension. Total: AED 650 (diagnostic + connector service).
Why previous shops missed it:
If you experience any of these patterns, you likely have an intermittent electrical issue:
Honest answer: Intermittent faults are time-intensive and unprofitable under the standard business model.
A garage that charges per-visit diagnostic fees makes money on quick diagnosis and parts replacement. An intermittent fault that requires 2-4 hours of data analysis, plus a week of vehicle monitoring, plus connector-level inspection doesn't fit the 30-minute-scan model.
Most shops aren't equipped, trained, or incentivized to solve intermittent faults. They scan, find nothing, and send you home. Not because they don't care — because their business model doesn't accommodate the time and tools required.
Q: How long does extended data logging typically take?
A: Most intermittent faults are captured within 3-7 days of monitoring. The vehicle is returned to you with a small data logger connected to the OBD port. You drive normally. When the fault occurs (or after the monitoring period), we download and analyze the data. Some faults with very specific trigger conditions may require 1-2 weeks.
Q: Will the data logger affect my car's operation?
A: No. The data logger passively reads information from the vehicle's communication bus. It doesn't send commands, modify settings, or affect any vehicle system. Your car operates exactly as normal during monitoring.
Q: Why can't the garage just drive my car until the fault appears?
A: For two reasons: (1) the fault may require conditions you experience but a technician doesn't (your commute route, your driving pattern, your parking conditions), and (2) a garage driving your car for days ties up a bay and a technician — impractical and expensive. Data logging lets you reproduce the fault in your normal driving conditions.
Q: What if the data logging period ends and the fault didn't occur?
A: We extend the monitoring period or adjust trigger parameters. If the fault truly doesn't occur during monitoring, we analyze what data was captured for subtle anomalies that haven't yet progressed to noticeable symptoms. In rare cases where monitoring is unsuccessful, you don't pay for the monitoring time — our No Fix, No Fee guarantee applies.
Q: Is this more expensive than a standard diagnostic?
A: The initial setup is comparable to a standard diagnostic fee (AED 500-900). If extended monitoring is needed, additional time is charged at diagnostic rates. However, the total cost is almost always less than the alternative: multiple failed diagnostic attempts at other shops, each costing AED 200-500 and replacing parts that weren't broken.
If your car has a real problem that multiple shops couldn't diagnose, the problem isn't your car — it's the diagnostic approach.
Equipment. Knowledge. Patience. MotorMec uses OEM-level data logging, extended monitoring, and systematic signal analysis to capture intermittent faults that standard scanning misses. We don't guess and we don't give up.
Report an intermittent fault for extended monitoring. WhatsApp us your symptoms, when they occur, and what previous shops have tried. We'll explain our monitoring approach and timeline before you commit.
No Fix, No Fee. If we can't isolate the root cause, you don't pay for diagnostic time. Intermittent faults are what we do.
Reviewed by [Lead Electrical Diagnostics Engineer], MotorMec Dubai. This article is based on 1,000+ intermittent fault diagnoses across European luxury vehicles in Dubai's extreme climate.
Last updated: February 2026
