Loose or improperly seated crankcase ventilation hose at the connection sensor; Damaged or corroded electrical connector at the sensor, causing an intermittent signal; Chafed or broken wire in the sensor circuit that shorts or opens intermittently; Failed crankcase ventilation hose connection sensor itself, with internal electronics that cut in and out; Cracked or deteriorated hose that allows movement and disrupts the sensor connection; Contamination or oil buildup on the sensor contacts, leading to erratic readings; PCM software glitch or faulty PCM driver circuit, though this is less common

DTC codes / P04xx · Auxiliary emission controls / P04E4

P04E4Crankcase Ventilation Hose Connection Sensor Circuit Intermittent/Erratic

P04E4 indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the crankcase ventilation hose connection sensor circuit. This sensor monitors whether the crankcase ventilation hose is properly connected, and the code sets when the signal momentarily drops out or jumps around instead of remaining steady.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or slight hesitation if the hose is partially disconnected and unmetered air enters the engine
Intermittent stalling at low speeds when the connection sensor signal fluctuates
A faint hissing or whistling noise from the engine bay if the hose is loose or cracked
Poor fuel economy or increased emissions due to crankcase ventilation disruption
In rare cases, a stored pending code that appears and disappears without the light staying on

Common causes, most likely first

Loose or improperly seated crankcase ventilation hose at the connection sensor
Damaged or corroded electrical connector at the sensor, causing an intermittent signal
Chafed or broken wire in the sensor circuit that shorts or opens intermittently
Failed crankcase ventilation hose connection sensor itself, with internal electronics that cut in and out
Cracked or deteriorated hose that allows movement and disrupts the sensor connection
Contamination or oil buildup on the sensor contacts, leading to erratic readings
PCM software glitch or faulty PCM driver circuit, though this is less common

How to diagnose and fix it

Inspect the crankcase ventilation hose and sensor connector for looseness, cracks, or oil residue, and reseat or clean as needed
Use a scan tool to view live data from the crankcase ventilation hose connection sensor while wiggling the connector and hose to reproduce the intermittent signal
Perform a voltage drop or resistance test on the sensor circuit wires, checking for opens or shorts while flexing the harness
Check the sensor's ground and reference voltage at the connector with a multimeter to confirm stable power and ground
Replace the crankcase ventilation hose connection sensor if electrical tests confirm it is faulty
Repair or replace damaged wiring and connectors, then clear the code and verify the repair with a test drive
If the code persists after all circuit and component checks, consult factory service information for PCM diagnostics or reflash procedures

Intermittent sensor signals often misdiagnosed

A loose oil filler cap or dipstick can create crankcase pressure changes that mimic a hose connection fault, so always check those simple items first.
The sensor circuit is often disturbed during unrelated engine repairs, so a recent service history can point to a connector that was not fully latched.
Technicians sometimes replace the sensor when the real problem is a chafed wire hidden inside the loom, so flex testing the harness is essential.
This code can set from a momentary glitch that never returns, so clearing it and test-driving may be all that is needed if no other symptoms exist.
Aftermarket air intake or breather modifications can alter crankcase ventilation flow and trigger intermittent connection sensor codes on otherwise healthy engines.

Can I keep driving with P04E4?

The vehicle is generally safe to drive with this code because it rarely affects engine operation, but avoid ignoring it if rough running or stalling occurs. Have the circuit inspected soon to prevent a minor connection issue from becoming a larger repair.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.