DTC code
P3191
Variable Intake Manifold Valve Stuck Open
Label auto-translated from another language and machine-checked. On manufacturer-specific codes the meaning can differ per platform — confirm with the scanner on the actual ECU.
Technical guide
Symptoms
- Engine cranks (spun by the hybrid system) but fails to start
- rough running or stalling
- MIL illuminated
- on Prius the vehicle may enter ready-off mode
- hybrid battery works harder to compensate
- risking deep discharge and overheating with repeated start attempts.
Probable causes
- Running out of fuel or low fuel pressure
- dirty/contaminated MAF sensor
- dirty throttle body (varnish buildup restricting airflow)
- detached vacuum hose (reported common on 2010-2011 Prius)
- failed fuel pump (reported especially on 2001-2003 Prius)
- clogged fuel filter or faulty injectors
- weak or depleted 12 V auxiliary battery / loss of power to the hybrid control module
- outdated ECU software on early Gen 2 Prius
- air induction system malfunction.
Diagnostic steps
- Confirm the tank actually has fuel — running out of fuel is one of the most commonly reported triggers.
- Read all codes (engine + hybrid systems) and freeze-frame data; check the 12 V auxiliary battery condition and connections.
- Inspect the air induction system: remove and inspect the MAF sensor for dust/debris and clean it; inspect vacuum hoses for detachment (especially 2010-2011 Prius).
- Clean the throttle body plate and bore of varnish/buildup.
- Test fuel pressure/fuel pump output; on 2001-2003 Prius a weak pump is a known failure (per source, the fuel tank assembly is replaced with the pump on those models).
- Check spark plugs and ignition.
- On early Gen 2 Prius, verify ECU software is current.
- Avoid repeated start attempts during diagnosis — each attempt cranks the engine via MG1 (approximately 15 seconds per attempt per source) and can drain the high-voltage battery.
- Clear codes and confirm reliable engine starts.
Cross-checked technical synthesis (QA). It does not replace the manufacturer's procedure.
Models most reported with this code (NHTSA)
Count of distinct owner complaints mentioning the code. US data — same engines, same failures.
AI here is a librarian: this page shows only what mechanics confirmed, or says “unknown”. It never suggests a diagnosis — MECCANIC interprets the code, never your car.
0 confirmed cases on P3191
Nothing confirmed yet for this code. No guess is offered on purpose.
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