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What Does 0 DTC Mean on a Check Engine Scanner?
What “0 DTC” Means
When your Autel scanner shows “0 DTC,” the ECU has no stored Diagnostic Trouble Codes at that moment. That doesn’t guarantee everything’s perfect—it just means no confirmed faults have met the threshold to be saved as codes.
0 DTC simply means there are no stored trouble codes.
Why the Check Engine Light Can Still Be On
- Pending codes: Detected once, not yet confirmed. Autel tools reveal these easily.
- Permanent codes: Emissions-related; remain until a successful drive cycle verifies repair.
- Readiness monitors not ready: Common after battery disconnect/reset.
- Non-powertrain/network issues: Basic readers may miss them; higher-end Autel tools won’t.
- Low voltage/communication glitches: Battery issues can confuse diagnostics.
Check engine light may stay on with 0 DTC if monitors aren’t ready.
Code Types at a Glance
| Type | Meaning |
| Stored (Confirmed) | Typically illuminate the MIL |
| Pending | Awaiting confirmation; may not light the MIL |
| Permanent | Persist until verified fixed via drive cycles |
| History | Previously recorded but not currently active |
How to Diagnose “0 DTC” with an Autel Scanner
1. Read all code categories: View Stored, Pending, Permanent, and History.
2. Check readiness monitors: Ensure monitors are complete before inspection.
3. Open Mode $06 (On-Board Monitoring): Spot developing faults (misfire counts, O₂ tests) before they set codes.
4. Watch live data: Fuel trims, ECT, O₂/AFR activity, misfire counters at idle and during a short drive.
5. Run active tests (bi-directional): Command fans, EVAP purge, injectors, etc., to pinpoint faults.
6. Inspect basics: Battery SOC, gas cap seal, vacuum hoses, intake tract, connectors.
7. Drive and rescan: If real, a fault often reappears as pending/confirmed within 1–2 trips.
Recommended Autel Scanners (Pick by Use Case)
Best All-Round DIY/Prosumer: Autel MK900BT
Why: Fast Android tablet platform, wide coverage, wireless Bluetooth VCI, live data graphing, Mode $06, readiness at a glance.
Great for “0 DTC” cases: Quickly surfaces pending/permanent codes and incomplete monitors; easy EVAP/gas-cap checks.
Nice add-ons: Works with BT506 (battery tests) and MV108S (videoscope) for deeper checks.
Shop-Level Diagnostics: MaxiSys Ultra S2
Why: Topology mapping, fast processor, extensive OE-level functions, strong bi-directional control.
For “0 DTC”: Dive into network modules that a basic reader misses; analyze Mode $06 and advanced live data across systems.
High-Value Pro Tablet: MaxiSys Elite II Pro
Why: OE-level diagnostics and active tests at a more approachable price point than flagship units.
For “0 DTC”: Reads manufacturer-specific codes, runs actuator tests to surface issues before they store.
Advanced Keys + Diagnostics: IM608 PRO II
Why: Combines robust diagnostics with key programming/IMMO capability.
For “0 DTC”: If immobilizer/anti-theft quirks cause no-start with no codes, this tool’s data + IMMO functions help isolate it.
Helpful Accessories
BT506 Battery Tester: Low voltage can mask faults and cause odd “0 DTC” behavior—test and document battery health.
MV108S Videoscope: Inspect EVAP hoses, intake leaks, and connectors without teardown.
Common “0 DTC” Scenarios and What to Do
- CEL on, 0 DTC → Suspect EVAP: Tighten/replace gas cap, inspect EVAP lines with MV108S, run a complete drive cycle, recheck monitors.
- Rough idle, 0 DTC: Check fuel trims on your Autel; high positive trims → vacuum leak, negative → rich condition.
- Battery recently disconnected: Expect Not Ready monitors; complete the manufacturer drive cycle and rescan.
CEL on with 0 DTC often points to EVAP—check the gas cap, hoses, and rerun a drive cycle.
When to See a Pro
If symptoms persist (stalling, poor power, hard starts) or the light stays on with no codes, a shop using MaxiSys Ultra S2 or Elite II Pro can perform deep bi-directional tests, smoke/pressure testing, and system-level analysis.
Quick FAQ
Does “0 DTC” mean my car is fine?
Not necessarily—there may be pending or permanent issues.
Can Autel scanners check emissions readiness?
Yes—monitor status is shown clearly, so you can confirm before testing.
Why did a code vanish?
Intermittent faults can clear; check History and Permanent sections to track them.
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