This BMW-specific code indicates a communication or control fault in the glow plug module – typically a wiring issue, a failed module, or a CAN bus problem. Often straightforward and relatively inexpensive to resolve.
P164B on a BMW diesel is a manufacturer-specific code that indicates the ECU has lost communication with or detected a fault in the glow plug control module. The most common cause is a poor connection or a failed module – not individual glow plugs. Diagnosis is straightforward and should be done cheapest-first.
Don't assume the module needs replacing – a simple wiring check is always the first step. Full diagnostic order below.
P164B is a BMW-specific fault code that indicates the engine control unit (ECU) has detected a communication or control fault with the glow plug control module – sometimes called the glow plug relay or glow plug controller. The module is responsible for supplying power to the glow plugs for cold starts and post-heating during warm-up. The ECU communicates with the module via a data bus (often BSD – Bit Serial Data) and monitors its status. When the ECU loses communication, receives invalid data, or detects an internal fault in the module, it sets P164B. Crucially, the code describes a communication or control fault, not a hardware failure of the glow plugs themselves. The problem could be a poor connection, a broken wire, a blown fuse, or a failed module. This code appears across BMW diesel families – from the N47 and B47 four‑cylinder units to the N57 and B57 six‑cylinder engines – and the diagnostic approach is essentially identical.
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 |
|---|---|---|---|
| Wiring/connector fault (BSD communication line) | Very High | £80–£200 | Check the module connector for corrosion, broken wires, or loose pins |
| Blown fuse or faulty relay | High | £80–£150 | Check the fuse box – the cheapest possible fix |
| Failed glow plug control module | Medium | £350–£500 | Replace only after ruling out fuses and wiring |
| ECU software/communication bus fault | Low | £150–£400 | Rare; may require software update or ECU reprogramming |
Cost figures [PATTERN DATA] – indicative independent BMW specialist pricing, not drawn from our engine replacement dataset.
Locate the glow plug control module fuse and relay in the engine bay fuse box. A blown fuse is a simple fix.
Visually check the harness to the module for chafing, breaks, or corrosion. Wiggle the connector while monitoring live data.
Check for power supply and ground at the module. If they're present but no communication, the module is likely faulty.
If fuses, wiring, and power are good, the module itself is the most likely failure point.
Our diagnostic wizard walks the same order, or confirm your engine with the registration lookup.
Yes, but cold starts will be difficult. P164B does not cause immediate engine damage, but if the glow plugs aren't heating, the engine may struggle to start in cold weather. Once started and warmed up, the car will run normally. However, prolonged hard starting can stress the battery and starter motor. Get it diagnosed before winter sets in, but it's not an emergency in warmer months. If the engine won't start at all, the fault may be more severe – have it recovered.
Yes, but cold starts will be difficult. Once the engine is warm, it runs normally. Avoid repeated hard starting to protect the battery and starter. Get it diagnosed soon.
No. A wiring issue or a blown fuse is far more common – both much cheaper than a new module. Always check those first.
Only temporarily. The code will return as soon as the ECU runs the glow plug system test, typically on the next cold start. Clearing it erases freeze‑frame data that helps with diagnosis.
Expect 1–2 hours of diagnostic time at an independent BMW specialist, typically £100–£200. Many specialists will waive or offset this if you proceed with the repair.
Glow plug systems are generally not covered by recalls, but some models had extended warranties on the glow plug module. Check your VIN against BMW UK recalls or use our recall checker.
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