P0542
Intake Air Heater "A" Circuit High
- Severity
- Low
- Driving
- Drivable — book it in
The intake air heater "A" circuit is reading high - typically shorted to voltage or a lost earth. The heater will not work properly, which shows up as hard cold starting and little else.
Possible causes
- CommonFailed intake air heater element
- CommonFailed heater relay
- CommonCorroded connections at the heater - it carries a very high current
- PossibleBlown fuse or fusible link
- PossibleDamaged wiring
- RareFailed control module driver
What you might notice
- Hard starting when cold
- White smoke on a cold start
- Rough running for the first minute
- Poor cold performance
- No symptom at all in warm weather
What to check, in order
- Check whether the high reading persists with the relay removed.
- Test on a genuinely cold engine. In warm weather a diesel will usually start acceptably without the intake heater, which is why these faults go unnoticed until winter.
- Check the fuse or fusible link and the relay - these circuits carry very high current and their connections suffer for it.
- Inspect the heater terminals for corrosion and heat damage.
- Measure the heater element resistance against specification.
- Check for voltage at the heater during a cold start.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Vehicle speed control, idle control and auxiliary inputs
P0500P0501P0502P0503P0504P0505P0506P0507P0508P0509P0510P0511P0512P0513P0514P0515P0516P0517P0518P0519P0520P0521P0522P0523P0524P0525P0526P0527P0528P0529P0530P0531P0532P0533P0534P0535P0536P0537P0538P0539P0540P0541P0542P0543P0544P0545P0546P0547P0548P0549P0550P0551P0552P0553P0554P0555P0556P0557P0558P0559P0560P0561P0562P0563P0564P0565P0566P0567P0568P0569P0570P0571P0572P0573P0574P0575P0576P0577P0578P0579P0580P0581P0582P0583P0584P0585P0586P0587P0588P0589P0590P0591P0592P0593P0594P0595P0596P0597P0598P0599