U3018: Korrelation zwischen Stromkreis A und B der Eingangsversorgung des Steuergeräts
Was zu tun ist
Have the battery and its connections tested before anything else is touched — including the battery terminals themselves, cleaned and retightened.
That sounds too simple for a code like this, and it is still the right first step: a battery weak enough to sag while cranking, or a terminal corroded under a clamp that looks perfectly tight, produces this entire family of faults exactly. It is the cheapest thing to rule out and the most common cause by a distance.
If the car has a page of unrelated warning lights, expect most of them to clear when this is fixed. A module with a poor supply reports nonsense about everything it watches, so one bad connection can light up half the dashboard.
Mention two things: whether the car has had a flat battery or a jump start recently, and whether any bodywork or accessory fitting has been done. A body shop that bolts an earth strap onto fresh paint makes a connection that looks perfect and conducts badly — and that is a classic cause.
Was dieser Code bedeutet
Two of the control module's input power circuits disagree with each other.
This range is different from every other network family, and the difference decides how it should be diagnosed.
U01xx and U02xx say a module went silent. U04xx and U05xx say a module is talking nonsense about something it watches. This range says a module is reporting a problem with its own foundations — its supply, its earth, or the ignition state that tells it whether the car is even meant to be awake.
Which makes these codes upstream of almost everything else. A module with a marginal earth does not fail cleanly; it reports implausible values about every sensor it reads, sets codes in unrelated systems, and drops off the bus intermittently. A scan tool showing thirty codes across five systems very often has one of these underneath it.
So read this family first and fix it first. Clearing a page of downstream codes before the supply fault is repaired produces a page of downstream codes again by the end of the week.
And start with the battery, genuinely. Not as a formality — a twelve-volt battery weak enough to sag during cranking, or a terminal with corrosion under a clamp that looks tight, reproduces this entire family exactly. It is the cheapest thing to eliminate and by some distance the most common cause.
A correlation code compares two things that should always match, and this one compares power feeds A and B.
The comparison exists because a module with redundant supplies must know when one has quietly gone. Both feeds should show the same system voltage, rising and falling together as the alternator loads and unloads. When one sits meaningfully lower than the other, the module has found a resistance in one path that the other does not have.
Which makes this the most useful code in the family, and it is worth saying why. Most supply faults present as "something is wrong somewhere"; this one has already narrowed the fault to one of two named circuits and proven the other is healthy. Everything the good feed shares — the battery, the main earth, the alternator — is thereby exonerated.
So the work is a voltage comparison between the two feeds at the module connector, under load. The one that sags is the one with the fault, and it will be a fuse holder, a connector, or a splice rather than the module.
A note on the sibling code. The corpus does not carry the B/C correlation code at U3019: two independent sources name different circuit pairs for it, and a code whose subject cannot be settled stays unwritten rather than guessed.
Wahrscheinliche Ursachen
Hier anfangen
- Zu niedrige Systemspannung · einfach
- Masseverbindung korrodiert · mittel
- Sicherung durchgebrannt oder Versorgung ausgefallen · einfach
- Versorgung oder Masse des Steuergeräts ausgefallen · mittel
- Korrodierter oder loser Stecker · einfach
Seltener
- Kabelbaum beschädigt · mittel
Symptome
Beteiligte Bauteile
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