P2605: Réchauffeur d'air d'admission B — circuit ouvert
Que faire
The car will still start, but expect it to be harder work on cold mornings — longer cranking, more white smoke, and rough running for the first thirty seconds or so. In warm weather you may notice nothing at all.
This is the second of two or three heater elements, which is why it degrades starting rather than preventing it. It is worth fixing before winter rather than after, since the remaining elements are then doing the whole job.
One thing to ask for specifically: have the relay and the heavy cable connections been tested under load? This circuit carries an enormous current — similar to a starter motor — so burnt relay contacts and a loose or corroded cable terminal are far commoner than a failed heater. A resistance check with a meter will not find those, because a bad joint can measure perfectly at low current and still collapse under eighty amps. The right test is a voltage-drop measurement while the heater is running.
Ce que signifie ce code
An open circuit in the control or supply of the second intake air heater element. The first is heater A, at P0540–P0543 and P2604.
Why there are two is the useful part, and it is entirely about current. An intake air heater — a grid heater on most diesels — warms the air entering the engine so that a cold cylinder reaches a temperature at which diesel will ignite. Warming that much air takes real power: a single element commonly draws fifty to a hundred amperes or more, which is the same order as a starter motor and far beyond what any ordinary engine circuit carries. Splitting the job across two or three elements, each with its own heavy cable and its own relay, is how that load is made survivable.
The consequence for diagnosis is that this is a high-current circuit pretending to be a control circuit, and it must be treated as one. Faults concentrate where current concentrates: burnt or pitted relay contacts, a heavy cable terminal that has loosened and heated, a corroded stud on the heater itself. The element is rarely the problem.
Resistance measurement is the wrong test here and it is the one people reach for. These elements measure well under an ohm in good health, so a meter cannot usefully distinguish a sound one from a degraded joint — and a connection that reads fine at the milliamp a multimeter passes can drop several volts at eighty amperes. The test that finds it is voltage drop under load: measure across each connection while the heater is actually working. That is the difference between a five-minute diagnosis and a replaced part that changes nothing.
One element failing usually leaves the vehicle starting, just less well — more cranking on a cold morning, more white smoke, rougher running for the first half-minute. That is exactly why this code is easy to live with and then forget, and why it is often found during an emissions test rather than by the driver.
Causes probables
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