P316A – Engine Coolant Temperature Signal Stuck High (BMW)

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By Reinier (Contact Me)
Last Updated 2023-06-27
Automobile Repair Shop Owner
CodeFault LocationProbable Cause
P316A Engine Coolant Temperature Signal Stuck High (BMW)
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Table of Contents

  1. What Does Code P316A Mean?
  2. Where is the P316A sensor located?
  3. What are the common causes of code P316A?
  4. What are the symptoms of code P316A?
  5. Get Help with P316A

What Does Code P316A Mean?

OBD II fault code P316A is a manufacturer-specific trouble code that is defined by carmaker BMW as P316A – “Engine Coolant Temperature Signal Stuck High”, and is set when the DME (Digital Motor Electronics) detects a persistently abnormal high voltage in the engine coolant temperature sensor’s signal circuit.

Engine coolant temperature sensors do more than provide a driver with a visual indication of the engine’s temperature. Engine coolant temperature sensors are in fact, critically important components in all modern engine management systems because these sensors provide the primary information that engine management systems on gasoline engines use to calculate appropriate ignition timing and fuel delivery strategies when an engine is cold. In the case of diesel engines, engine coolant temperature sensors provide glow plug control modules with the primary information these modules use to control the glow plugs on cold engines.

In terms of operating principles, engine coolant temperature sensors are typically known as Negative Temperature Coefficient (NTC) thermistors, which means that their internal electrical resistance decreases in an almost linear relationship with the increasing temperature of the engine coolant. As a practical matter, the DME supplies the sensor with a 5-volt reference voltage that passes through a resistive element in the sensor, so when the engine is cold, the DME expects to see a specified voltage as a result of the high resistance in the sensor.

Thus, as the engine coolant’s temperature rises, the resistance in the sensor decreases, meaning that the voltage that is returned to the DME also changes, and in a fully functional sensor, the changing signal voltage will be an accurate reflection of the coolant’s temperature. This information is crucially important because the DME needs to enrich the air/fuel mixture to compensate for the poor combustion properties of gasoline in cold engines. Moreover, the DME also needs to adjust the ignition timing after cold starts to improve combustion further and to establish and maintain a stable idling speed.

However, since enriching the air/fuel mixture increases the load on catalytic converters that may take time to enter closed-loop operation the DME monitors the signal voltage from the coolant temperature sensor continuously as the engine warms up. During this time, the DME makes small but continuous changes to the air/fuel mixture because as the engine warms up, combustion improves progressively to the point where enrichment is no longer required. This point is usually reached when the engine coolant reaches a temperature of 104 deg F, at which point the DME also returns the ignition timing to its base or reference setting.

Based on the above, it should be clear that the DME expects to see a progressive change in the engine coolant temperature sensor’s signal voltage from the time the engine starts to the point where the engine reaches its optimal operating temperature, at which point the signal voltage should stabilize and only fluctuate in response to the duty cycle of the radiator cooling fan(s).

So, in the case of code P316A, a persistent high signal voltage means that the coolant temperature sensor is not responding to changes in the temperature sensor’s temperature. If this happens, the DME will set code P316A and illuminate a warning light. In most instances of this code, and particularly on engines with mapped (computer-controlled) thermostats, the DME may also initiate a fail-safe or limp mode as a means to prevent the engine from overheating.

Note that on engines with conventional thermostats, the engine coolant temperature sensor is sometimes involved in the control and management of the radiator cooling fans, although most modern engines have multiple engine coolant temperature sensors, one or more of which may control the radiator cooling fans directly.

Where is the P316A sensor located?

This image shows the location (arrowed) of the engine coolant temperature sensor on BMW E91, E92, and E93 models. Note, though, that since both the appearance and location of coolant temperature sensors vary greatly between different BMW models, we strongly recommend that you research the exact location of all the coolant temperature sensors on an affected vehicle to avoid misdiagnoses and the possible unnecessary replacement of parts.

NOTE: Be aware that removing coolant temperature sensors from some BMW engines could cause the loss of significant amounts of engine coolant. Also, be aware of the fact that replacing lost coolant requires that all air be purged from the cooling system through a dedicated bleed screw. However, the process of purging air from a hot engine carries a significant risk of sustaining serious burns and scalds, so be sure to observe all safety precautions, or seek professional assistance with diagnosing and repairing coolant temperature sensor issues.

WARNING: Note that the cooling systems of many modern BMW vehicles can only be refilled and purged of air with the aid of special equipment that evacuates the cooling system and refills the system at the same time. Failure to use this equipment could result in low coolant levels, air locks in the system, and poor coolant circulation that will almost certainly cause the engine to overheat, which usually causes severe to fatal engine damage.

What are the common causes of code P316A?

Common causes of code P136A could include one or more of the following-

  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or electrical connectors in the coolant temperature sensor’s wiring
  • Defective or malfunctioning engine coolant temperature sensor
  • The use of a substandard aftermarket sensor
  • The use of an incorrect or unsuitable coolant temperature sensor
  • Airlocks or low coolant level; since the tip of the sensor is meant to be immersed in coolant to work correctly, an airlock or a low coolant level could cause the sensor not to react to changes in the coolant’s temperature
  • Blown fuse(s)
  • Malfunctions or defects in a shared 5-volt reference circuit; in some cases, multiple engine sensors share a common reference voltage circuit, which means that if a shared reference voltage circuit fails, all the sensors that share that circuit will also stop working

What are the symptoms of code P316A?

Some common symptoms of code P136A could include one or more of the following-

• Stored trouble code and an illuminated warning light
• Depending on the nature of the problem, multiple additional codes may also be present, with engine temperature-related codes being the most common
• The vehicle may be in a fail-safe or limp mode to protect the engine against overheating
• The A/C system may be deactivated, and the radiator cooling fan(s) may run continuously to reduce the load on the engine cooling system
• The engine may overheat fatally
• The temperature gauge in the dashboard may display erratic readings

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