One of the most common electrical system fault codes on Mercedes. It means the ECU is detecting low system voltage — and it can cause a cascade of other issues if ignored.
P0562 means the ECU is detecting system voltage below the minimum threshold — typically below 10V while the engine is running. On most Mercedes, this is a battery or charging system issue, not a catastrophic failure. It should be diagnosed cheapest-first.
Do not let anyone sell you a new ECU before the battery and charging system have been properly tested. Full diagnostic order below.
The ECU monitors the vehicle's system voltage via the battery voltage input. When the engine is running, the alternator should maintain system voltage between approximately 13.5V and 14.5V. P0562 is set when the ECU detects voltage below a critical threshold (typically around 10V) for a set period. Crucially, the code describes a voltage problem, not a specific component failure. The voltage could be genuinely low due to a weak battery, a failing alternator, or a wiring issue. That distinction is the entire difference between a £100 battery and a £800 alternator replacement. This code appears across the full range of Mercedes petrol and diesel engines, from the OM651 diesel to the M276 petrol V6, and the diagnostic approach is essentially identical regardless of which engine triggers it.
Ordered by how often each turns out to be the real culprit — with typical fitted cost against each, so you can sanity-check any quote you've been given.
| Cause | Likelihood | Typical Cost (fitted) | Notes |
|---|---|---|---|
| Weak or failing battery | Very High | £100–£250 | Most common — battery may be old or discharged |
| Loose or corroded battery terminals | High | £50–£100 (clean/repair) | Poor connection causes voltage drop |
| Failing alternator | Medium | £400–£800 | Alternator not charging at full capacity |
| Drive belt slipping or worn | Medium | £150–£300 | Belt slip reduces alternator output |
| ECU or wiring issue | Low | £600–£1,200 | Rare — rule out battery and alternator first |
Cost figures [PATTERN DATA] — indicative independent-specialist pricing, not drawn from our engine replacement dataset.
With the engine off, measure battery voltage. A healthy battery should read 12.5V or more. If it's below 12V, it needs charging or replacement.
Look for corrosion, loose connections, or damaged cables. A simple clean and tighten may fix the issue.
With the engine running, measure voltage at the battery. It should be 13.5–14.5V. If it's below 13V, the alternator may be faulty.
Inspect the belt for cracks, glazing, or looseness. A worn belt can slip and reduce alternator output.
If battery and alternator are both good, the ECU's voltage sensing circuit or wiring may be at fault.
Our diagnostic wizard walks the same order, or confirm your engine first with the registration lookup.
Conditionally, yes — but you should get it checked soon. P0562 on its own is not an engine-destroying fault, but if the battery is not being charged, you risk being stranded. If the voltage drops too low, the ECU may shut down non-essential systems and the engine may eventually stall. If the battery warning light is on and the engine is running, get the alternator tested as soon as possible. Short journeys are okay, but avoid long trips until the cause is identified.
Yes, for short journeys, but get it checked soon. If the battery is not being charged, you risk being stranded. Avoid long trips until the cause is identified.
No. In many cases, it's a weak battery or a loose connection. Always diagnose cheapest-first.
Only temporarily. The code will return as soon as the ECU detects low voltage again. Clearing it also destroys the freeze-frame data a specialist would use to narrow the cause.
Expect one hour of diagnostic time at an independent Mercedes specialist. Many will offset that cost against the repair if you proceed with them.
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