Symptom
Vehicle charges more slowly than usual
The car still charges, but at a lower rate than it used to — a full charge takes noticeably longer, or a rapid charger delivers far less than its rating. The car rarely says why, which is what makes this worth recognising as a symptom in its own right.
Most often it is the vehicle protecting something, not the charger failing. Charging generates heat in the battery, the on-board charger and the DC/DC converter, and if any of those cannot be cooled properly the car reduces the rate rather than refusing outright. So a failed electronics coolant pump, low coolant in the electronics circuit, or a temperature sensor reading wrongly can all present as nothing more than slow charging — and nobody connects a slow charge to a coolant pump.
Several ordinary explanations should be ruled out first, because they are not faults at all. A cold pack charges slowly by design and warms as it goes. A nearly full pack tapers deliberately in the last quarter. A shared rapid charger splits its output between two cars. And a domestic supply, an extension lead or a long cable will each cap the rate well below what the vehicle could take.
Compare against a different charger before assuming the car is at fault — that one test separates the vehicle from the supply, and it is free.
Also described as: charging slowly, slow charging, charges slower than it used to, takes longer to charge, reduced charging rate, rapid charging slow, charge rate limited, will not fast charge, شارژ کند شده, دیر شارژ میشود, carga mas lento, tarda mas en cargar, carga lenta, الشحن بطيء, يأخذ وقت أطول في الشحن, الشحن أبطأ من المعتاد
What this usually means
Most of this is the vehicle protecting something rather than the charger failing, and several versions are not faults at all. Charging generates heat in the pack, the on-board charger and the DC/DC converter, and if any of those cannot be cooled the car reduces the rate rather than refusing outright — so a failed electronics coolant pump can present as nothing more than a slow charge, and nobody connects the two.
Temperature is the largest single variable and it is published. The full rate is available only in a window of roughly 20 to 40 °C pack temperature. Below about 10 °C the management reduces power sharply, because a cold cell has higher internal resistance and its chemistry runs slower — pushing current into it anyway is what causes lasting damage. That is why a rapid charge on a winter morning delivers a fraction of the rating.
Preconditioning is the answer and it usually has to be triggered. Most vehicles heat the pack for rapid charging only when a rapid charger is set as the navigation destination — so a driver who navigates by phone and arrives at a charger with a cold pack gets the slow charge and no explanation.
The taper is deliberate too. The rate falls away in the last quarter so every cell can be brought to the same voltage, which is the balancing the pack depends on. A session judged from 80 to 100 per cent will always look slow.
Compare against a different charger before assuming the car is at fault. A shared rapid charger splits its output, a domestic supply caps it, and an extension lead or a long cable each cost more than people expect — and that one test is free.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Slow in cold weather, normal once warm | Pack temperature outside the window — below about 10 °C the management reduces power to protect the cells | Read live pack temperature at the start of the session. The full rate needs roughly 20 to 40 °C. | Precondition before rapid charging, which on most cars means setting the charger as the navigation destination rather than just driving there. |
| Slow only above roughly three-quarters charge | The deliberate taper — the rate falls so every cell can be brought to the same voltage | Compare the rate at low state of charge against the rate near full. Judging a session by its last quarter always looks slow. | No repair. Rapid-charge to 80 per cent and drive on; the last fifth costs disproportionate time by design. |
| Slow at every charger including known-good ones | The vehicle — on-board charger, cooling for it, or a thermal management fault | Try a different charge point first; that separates vehicle from supply for nothing. Then read charger and converter temperatures live. | Diagnose the on-board charger or its cooling. Check the electronics coolant circuit, which is separate from the engine's. |
| Slow with a cooling fan or pump running hard, or not running at all | A cooling fault — the car derates rather than refusing, so the symptom is slowness rather than a warning | Check the electronics coolant reservoir and confirm the pump runs. Inspect the pack's cooling intake for blockage. | Renew the pump, bleed the circuit properly, clean the intake. A slow charge is a strange way for a coolant pump to announce itself. |
| Slow at one location only | The supply — a shared rapid charger splitting output, a domestic circuit, a long cable or an extension lead | Try another charge point. Check whether a second car is plugged into the same unit. | No vehicle repair. Use a different supply, or have the domestic installation assessed if it is consistently below its rating. |
| Slow since a cable or adapter was changed | The cable is telling the car it can carry less — its rating is coded in the plug | Compare against the original cable. The coding pin in the plug caps the current regardless of what the supply could give. | Use a correctly rated cable. This is a specification issue rather than a fault. |
-
Slow in cold weather, normal once warm
- Likely cause
- Pack temperature outside the window — below about 10 °C the management reduces power to protect the cells
- How to confirm it
- Read live pack temperature at the start of the session. The full rate needs roughly 20 to 40 °C.
- What fixes it
- Precondition before rapid charging, which on most cars means setting the charger as the navigation destination rather than just driving there.
-
Slow only above roughly three-quarters charge
- Likely cause
- The deliberate taper — the rate falls so every cell can be brought to the same voltage
- How to confirm it
- Compare the rate at low state of charge against the rate near full. Judging a session by its last quarter always looks slow.
- What fixes it
- No repair. Rapid-charge to 80 per cent and drive on; the last fifth costs disproportionate time by design.
-
Slow at every charger including known-good ones
- Likely cause
- The vehicle — on-board charger, cooling for it, or a thermal management fault
- How to confirm it
- Try a different charge point first; that separates vehicle from supply for nothing. Then read charger and converter temperatures live.
- What fixes it
- Diagnose the on-board charger or its cooling. Check the electronics coolant circuit, which is separate from the engine's.
-
Slow with a cooling fan or pump running hard, or not running at all
- Likely cause
- A cooling fault — the car derates rather than refusing, so the symptom is slowness rather than a warning
- How to confirm it
- Check the electronics coolant reservoir and confirm the pump runs. Inspect the pack's cooling intake for blockage.
- What fixes it
- Renew the pump, bleed the circuit properly, clean the intake. A slow charge is a strange way for a coolant pump to announce itself.
-
Slow at one location only
- Likely cause
- The supply — a shared rapid charger splitting output, a domestic circuit, a long cable or an extension lead
- How to confirm it
- Try another charge point. Check whether a second car is plugged into the same unit.
- What fixes it
- No vehicle repair. Use a different supply, or have the domestic installation assessed if it is consistently below its rating.
-
Slow since a cable or adapter was changed
- Likely cause
- The cable is telling the car it can carry less — its rating is coded in the plug
- How to confirm it
- Compare against the original cable. The coding pin in the plug caps the current regardless of what the supply could give.
- What fixes it
- Use a correctly rated cable. This is a specification issue rather than a fault.
Codes that produce this symptom (354)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0B38 Motor Electronics Coolant Pump B Control Circuit/Open Typical of this code High
- P0B3A Motor Electronics Coolant Pump B Control Circuit High Typical of this code High
- P0BBF Hybrid/EV Battery Pack Cooling Fan Supply Voltage Circuit/Open Typical of this code High
- P0BC2 Hybrid/EV Battery Temperature Sensor E Circuit Typical of this code High
- P0BC3 Hybrid/EV Battery Temperature Sensor E Circuit Range/Performance Typical of this code High
- P0BC4 Hybrid/EV Battery Temperature Sensor E Circuit Low Typical of this code High
- P0BC5 Hybrid/EV Battery Temperature Sensor E Circuit High Typical of this code High
- P0BC6 Hybrid/EV Battery Temperature Sensor E Circuit Intermittent/Erratic Typical of this code High
- P0BC7 Hybrid/EV Battery Pack Cooling Fan 1 Sense Circuit/Open Typical of this code High
- P0BC8 Hybrid/EV Battery Pack Cooling Fan 1 Sense Range/Performance Typical of this code High
- P0BC9 Hybrid/EV Battery Pack Cooling Fan 1 Sense Circuit Low Typical of this code High
- P0BCA Hybrid/EV Battery Pack Cooling Fan 1 Sense Circuit High Typical of this code High
- P0BCB Hybrid/EV Battery Pack Cooling Fan 1 Sense Circuit Intermittent/Erratic Typical of this code High
- P0C32 Hybrid/EV Battery Cooling System A Performance Typical of this code High
- P0C33 Hybrid/EV Battery Temperature Sensor F Circuit Typical of this code High
- P0C34 Hybrid/EV Battery Temperature Sensor F Circuit Range/Performance Typical of this code High
- P0C35 Hybrid/EV Battery Temperature Sensor F Circuit Low Typical of this code High
- P0C36 Hybrid/EV Battery Temperature Sensor F Circuit High Typical of this code High
- P0C37 Hybrid/EV Battery Temperature Sensor F Circuit Intermittent/Erratic Typical of this code High
- P0C42 Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit Typical of this code High
- P0C43 Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit Range/Performance Typical of this code High
- P0C44 Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit Low Typical of this code High
- P0C45 Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit High Typical of this code High
- P0C46 Hybrid/EV Battery Pack Coolant Temperature Sensor A Circuit Intermittent/Erratic Typical of this code High
- P0C47 Hybrid/EV Battery Pack Coolant Pump A Control Circuit/Open Typical of this code High
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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- The car — make, model, year and engine. The same fault behaves differently on each.
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