P2606: Intake Air Heater B Circuit Range/Performance
What to do
Cold starting will be poorer than it should be — more cranking, more white smoke — and possibly nothing noticeable once warm or in summer.
Ask for the connections to be checked under load rather than just tested for continuity. This circuit carries a starter-motor-sized current, so a joint that measures perfectly with a meter can still be collapsing under real load, and a connection that has been quietly overheating usually looks discoloured once someone looks at it.
One thing to mention if it applies: a battery that keeps going flat. A heater relay that has welded closed leaves the element drawing enormous current whenever the ignition is on, and that combination — this code plus unexplained battery drain — points straight at it. Worth catching early, because it also puts continuous heat into a part not built for it.
What this code means
The second intake air heater circuit is electrically connected and not behaving as commanded — drawing the wrong current for the state it was put in, or failing to change the intake air temperature the way the module expected.
This is the code that catches a heater which is degraded rather than dead, and that distinction matters because a partly working grid heater is invisible to every simple test. The circuit is continuous, the relay clicks, the element is intact — and a corroded stud or a heat-damaged cable terminal is dropping enough voltage that the element never reaches useful temperature. The module notices because it is watching the result, not the connection.
The commonest physical finding is a connection that has been heating itself. A joint with a little resistance in a circuit carrying eighty amperes dissipates real power at that point, which oxidises it further, which raises the resistance again. It is a process that accelerates, so a connection found discoloured or with softened insulation around it is the fault rather than a symptom of it.
A heater stuck permanently on is the other reading of this code, and it is the one worth catching quickly. A welded relay contact leaves the element drawing its full current whenever the ignition is on — which flattens a battery in short order, loads the alternator continuously, and puts sustained heat into an intake manifold designed for intermittent warming. Unexplained battery drain on a diesel, alongside a code from this family, is a stuck heater relay until proven otherwise.
Likely causes
Start here
- High resistance in heater wiring · moderate
- Corroded or loose connector · easy
- Failed intake air heater relay · moderate
- Failed intake air heater element · moderate
Less common
- Poor module ground connection · moderate
Symptoms
Components involved
Information, not instruction
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