P1299 – Cylinder Head Overtemperature Protection Active (Ford, Lincoln, Mazda, Mercury)

By Reinier (Contact Me)
Last Updated 2017-03-31
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1299

Table of Contents

1. What Does Code P1299 Mean?
2. What are the common causes of code P1299?
3. What are the symptoms of code P1299?
4. How do you troubleshoot code P1299?
5. Codes Related to P1299
6. Get Help with P1299

What Does Code P1299 Mean?

SPECIAL NOTES: The exact definition of code P1299, or any other manufacturer specific trouble code for that matter, should ALWAYS be researched and verified to avoid confusion, misdiagnoses, and the unnecessary replacement of parts and/or components. In the case of P1299 specifically, there are hugely conflicting resources online that list this code with the definition “Cylinder Head Over-temperature Protection Active” for many applications, even though the application mentioned does not use P1299 at all.

Nonetheless, every reasonable effort has been made to verify that code P1299 is used by car makers Ford, Mercury, and Lincoln with the definition “Cylinder Head Over-temperature Protection Active”, to indicate engine over heating problems. Whenever code P1299 is encountered on any other application(s), verify the definition with the manual for that application, or consult the authorized dealer for detailed information on the definition of code P1299 as it applies to that application. END OF SPECIAL NOTES. 

OBD II fault code P1299 is a manufacturer specific code that is defined by Ford, Mercury, and Lincoln as “Cylinder Head Over-temperature Protection Active”, and on these applications, P1299 is set when the PCM (Powertrain Control Module) detects an engine overheating condition via a dedicated CHT (Cylinder Head Temperature) sensor and monitoring/control circuit. Note that the definition “Cylinder Head Over-temperature Protection Active” refers to both the facts that an overheating condition exists, and that the PCM has initiated a “Fail Safe” mode, which is a series of actions designed to prevent the engine from overheating further to help protect it against suffering potentially fatal damage.

In this type of engine temperature monitoring system, the dedicated CHT sensor is not in contact with the engine coolant, since in some cases, an engine can suffer fatal overheating within seconds if the engine loses its coolant, which is a circumstance that is not always reflected by the temperature gauge on the dashboard. For this reason, the dedicated CHT sensor obtains readings based on the temperature of the metal of the cylinder head, which is a more accurate indication of the engine’s actual temperature.

In terms of operation, the CHT sensor converts the temperature of the cylinder head into a signal voltage (or resistance) that changes as the temperature changes. The PCM then interprets the signal voltage (or resistance) as changes in temperature, and when it detects a temperature that exceeds a critical limit set by the manufacturer, it will set code P1299, illuminate a warning light, and initiate the Fail Safe mode.

In practice, the setting of code P1299 is largely independent of the cause(s) of the engine overheating, and the only thing the PCM is concerned with is preventing the engine from overheating further. To accomplish this, the PCM will reduce the load on the engine, typically by deactivating the A/C system, as well as by deactivating some opposing cylinders on V-type engines. When cylinders are deactivated, the PCM disables the spark plugs on those cylinders, as well as the fuel supply to affected cylinders to protect the catalytic converter(s). The deactivated cylinders then act as heat pumps, using the air that passes through them to absorb some of the engine’s heat, which is then expelled through the exhaust.

Other protective measures include entering limp mode, limiting throttle response to working cylinders, preventing some gearshifts on automatics, and in extreme cases, shutting the engine down and/or preventing the engine from starting until the problem has been resolved.

The image below shows a typical CHT sensor. Note that even though this particular example closely resembles a conventional Engine Coolant Sensor, the two types of sensor are NOT interchangeable. Also, note that the appearance, dimensions, location, and operating range of CHT sensors vary between applications.

What are the common causes of code P1299?

Since code P1299 sets independently of any particular cause (apart from a failure or malfunction of the CHT sensor or its control circuit) any problem, defect, malfunction, or failure of any component, part, system (or subsystem) that controls, monitors, or maintains the engine cooling system and/or temperature can either set P1299, or contribute to the code being set.

The list of primary causes of engine overheating is extensive, but almost all of the causes listed here are common to all applications. Typical causes could include the following-

• Loss of engine coolant foe any reason
• Poor circulation of coolant
• Insufficient air flow over, or through the radiator
• Defective thermostat
• Defective CHT sensor
• Damaged, burnt, shorted, disconnected, and or corroded wiring and connectors almost anywhere in the cooling system
• Open circuits almost anywhere in the cooling system
• Defective radiator cooling fan(s)
• Defective, or failed water pump
• Slipping, or failed water pump drive belt
• Exceeding the application’s rated towing, or load carrying capacity

NOTE: Apart from the obvious causes of engine overheating listed above, other causes such as incorrect VVT/VVC, and ignition timing base settings can contribute to engine overheating. However, these causes are largely specific to the engine involved, so consult the manual for that specific engine for detailed information on this type of issue.

What are the symptoms of code P1299?

Apart from a stored trouble code and an illuminated warning light, all applications share an overheated engine as a symptom of this code, although the degree of overheating (and resulting engine damage) varies between applications. Other possible symptoms may include the following-

• Loss of power as some cylinders are deactivated, and/or turbo boost is reduced
• Vehicle may enter limp mode with reduced throttle response, and limited functionality of the automatic transmission
• Engine may be shut down automatically
• Engine may be prevented from starting until the engine has cooled down, or until the root cause(s) of the code is/are resolved
• Repeated instances of P1299 can lead to blown cylinder head gaskets, cracked cylinder heads, increased oil consumption due to damaged piston rings, and other severe mechanical failures, such as engine seizure. However, be aware that one or more, or even all of these symptoms can result from a single instance of code P1299.

How do you troubleshoot code P1299?

SPECIAL NOTES: Note that while the Fail Safe system exists to minimize engine damage during an episode of overheating, some defects /malfunctions / failures in the cooling system can cause fatal engine overheating within mere seconds, and it must be understood that even if the PCM shuts the engine down, the damage is often already done by the time the engine is shut down. 

It must also be understood that some engines are more resistant to the effects of overheating than others; while some engines will survive multiple instances of severe overheating, others may suffer fatal damage at the first instance of only moderate overheating, which means that regardless of the degree of overheating on ANY engine, the entire engine cooling system MUST be checked with every instance of code P1299. Moreover, depending on the engine, some effects of severe overheating, such as the loss of spring tension in the piston rings, may take varying amounts of time to manifest in the form of increased oil consumption.

Therefore, and since all engines react differently to overheating, the following items MUST be checked during all instances of this code, and non-professional mechanics should be aware that some parts and components MUST be replaced in order to be reasonably sure that the problem will either not recur, or that some components that may have suffered damage during the overheating episode will not fail unexpectedly.     

Check list- (Only when the engine has cooled down)

• If the engine coolant level is low, check for obvious signs of leaks, and make repairs as required. Be aware though that some types of leaks may be extremely difficult to spot, so if there are no obvious leaks such as burst radiator hoses or holes in the radiator perform a pressure test with an approved pressure pump. Consult the manual on the correct procedure to perform this test.
• Check for the presence of engine oil in the coolant, or coolant in the engine oil. This is often easy to recognize as a milky white emulsion on the dipstick, or on the inside of the oil filler cap. However, depending on the site of the damage to a cylinder head gasket, such as between two cylinders, it is possible for the oil and coolant not to come into contact with each other. In these cases, a simple compression test will reveal the site of the damage. Consult the manual on how to interpret the results of a compression test correctly.
• Check for signs of oil or coolant seeping from under the cylinder head(s). This will often reveal itself as a damp area where the cylinder head and the engine block meet. Fluid seepage in this area is a sure sign that the cylinder head is warped, and replacement of the cylinder head is the only reliable remedy.
• If the engine coolant is not perfectly clear, remove the radiator and have it cleaned out professionally to remove rust, corrosion, and scale that prevent the coolant from circulating freely.

List of required replacements-

• Replace the oil and oil filter, since even moderate overheating can degrade engine oil to the point of uselessness.
• Replace the thermostat, since it is very difficult, if not impossible to determine if a defective thermostat was the cause or the result of the overheating episode. Bear in mind that the vast majority of engine overheating episodes are caused by defective thermostats, so do NOT assume that the thermostat did not cause the problem.
• Replace the water pump, since even moderate overheating can damage the pump’s mechanical seals, meaning that the pump can fail unexpectedly at any moment.
• Replace the timing belt and its tensioning device, since overheating can reduce the useful life of a timing belt by 50% or more. Timing belt failures can cause some engines to fail in dramatic fashion, so don’t risk it.
• Replace the transmission fluid since even moderate overheating can seriously degrade the fluid, which can (and usually does) result in major transmission failures.
• Replace the spark plugs, since severe overheating can cause the insulating material around the central electrode to crack. Pieces of this material that come adrift and fall onto a piston can cause severe or even fatal damage to the piston, piston rings, valves, and the cylinder head.

WARNING: Failure to perform the above steps and replacements means that there is no guarantee that the problem will not recur, even though the cause of the first instance of the code may have been found and corrected. The next occurrence of P1299 may very well be as the result of a failure to replace a previously damaged part or component, so play it safe, and prevent the problem from occurring again is so far as this is possible to do. END OF SPECIAL NOTES.

STEP 1

Record all fault codes, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: If any other codes are present along with P1299, note the order in which they were stored. All codes that precede P1299 must be investigated and resolved before an attempt is made to diagnose P1299. Codes that follow P1299 are likely to be result of P1299, as opposed to being the cause, or contributing factors.

Step 2

Refer to the SPECIAL NOTES at the start of this section.

Assuming there are no visible fluid leaks it is important at this point to see if the engine will start, and if it does start, to see how it runs. If the engine starts and it runs smoothly, do NOT allow it to warm up before confirming that the level of the coolant is up to the proper mark.

However, if the engine starts but it misfires, do NOT allow the engine to run for an extended period or to warm up before the cause of the misfire(s) is found and corrected. The engine can misfire for any number of reasons, and some of these reasons could involve serious mechanical or electrical issues caused by the overheating. Consult the manual for detailed information on possible mechanical or electrical failures due to overheating, and correct these issues before continuing the diagnostic procedure.

Step 3

If the engine starts and it runs smoothly, do NOT assume that it has not suffered damage. For instance, not all cylinder head gasket failures are immediately apparent, and in many cases, a specialized test, or series of tests is required to confirm, or eliminate the possibility of cylinder head gasket failure(s). Consult the manual on the tests that are required to diagnose damaged cylinder head gaskets, and the correct procedures to perform the recommended tests. Note however that the average non-professional mechanic will likely not own, or have easy access to the required test equipment- if this is the case; the better option is to refer the vehicle for professional diagnosis and repair.

If the vehicle is driveable, it is strongly recommended that it be removed to a specialist repair shop, or even the authorized dealer to have the required test(s) performed. Failure to do this could result in misdiagnoses, the unnecessary replacement of parts or components, and many hours of wasted diagnostic time. If on the other hand, the vehicle is not driveable or if the engine does not start, it is often more cost effective to refer the vehicle for professional diagnosis and repair, and especially so in the case of DIY mechanics who are not comfortable with the idea of diagnosing and repairing complex issues and problems.

NOTE: Typical tests include testing for the presence of hydrocarbons in the coolant, testing for anti-freeze contamination of the engine oil, a cylinder compression test, a cylinder leak down test, and in some cases, and oil pressure test.

Step 4

This and all subsequent steps will assume that the engine is known not to have suffered any damage, that all steps have been taken to repair all damage that may have occurred as a result of the overheating episode, and that all ancillary parts that can cause a recurrence of the problem have been replaced.

NOTE #1: Before proceeding with the diagnostic procedure, determine if the scanner has control functions; if it has, use the scanner to command the radiator cooling fan(s) on to run at both speeds, if the system is designed to work on two speeds. Note the fan RPM’s at both speeds, and compare the obtained reading(s) with the values stated in the manual. If a discrepancy of more than a few percent is found, but there are no fan related codes present, scan the system for pending codes that might indicate why the fan(s) is/are not working at the correct speed. Make repairs as required to ensure the fan(s) operate(s) at the correct speed before proceeding.

NOTE #2: If the application is fitted with moveable grille shutters, use the scanner to operate the shutters from fully closed, to the fully open position multiple times to ensure that there is not an intermittent fault present that interferes with the shutter’s operation. If the shutters do not work as designed, make repairs as required to ensure that they work as intended.

So, with all of the above said,  consult the manual to determine the location  of the CHT sensor, as well as the location, function, routing, and color coding of all associated wiring. Perform a thorough visual inspection of all wiring, and look for damaged, burnt, shorted, disconnected, and/or corroded wiring and connectors. Make repairs as required, clear all codes, and rescan the system to see if the code returns. Note that in some cases, it may be necessary to complete at least one complete drive cycle before the code can be cleared, or the system rescanned.

NOTE: When inspecting the wiring pay particular attention to the condition and tightness of the connector or if there is no connector attached directly to the sensor, the wires that exit the sensor. In the latter case, it is common for the conductor to break within the insulation, thus creating an open circuit that is not immediately visible or apparent. Open circuits at this point can cause the PCM to “think” that the engine is overheating, when it is not.

Step 5

If no visible damage to the wiring is found, prepare to perform reference voltage, ground, continuity, and resistance tests on all associated wiring. Be sure to disconnect the sensor from the PCM to avoid damage to the controller during this step.

Consult the manual on the correct procedure to test the sensor and associated wiring to obtain the most accurate results. Compare all obtained readings with the values stated in the manual, and replace the sensor if it does not conform to the manufacturer’s specifications, or repair/replace wiring to ensure that all electrical values fall within specified values and/or ranges.

NOTE: Only use OEM replacement sensors, since many aftermarket units do not offer the accuracy, durability, or sensitivity of OEM sensors, which can cause a recurrence of the code.

Step 6

If the CHT sensor is replaced, double check that all wiring is connected and secured, the engine coolant level is up to the correct mark, that all caps (oil, radiator, and/or expansion tank), are fitted properly, and that the engine oil is up to the mark before operating the vehicle to see if the code returns.

Complete at least one complete drive cycle with the scanner connected to monitor the engine temperature in real time. However, do not confuse the engine temperature with the engine coolant temperature- narrow the scanner’s monitoring function down to show only the CHT sensor’s live data to avoid obtaining the wrong information.

As a rule, the engine temperature (as measured by the CHT sensor) will rise steadily until the engine reaches its normal operating temperature, after which the reading should remain fairly constant within a narrow range until the engine cools down again. Any large temperature fluctuations while the engine is running are indicative of problems that could include bad electrical and/or ground connections anywhere in the engine cooling system, intermittent electrical problems that affect the operation of the radiator cooling fan(s), intermittent failures of the CHT sensor, issues with how the engine coolant circulates through the cooling system, or even defects within the PCM.

Identifying and correcting these types of problems can be extremely challenging and time consuming, which often means that the better option is referring the vehicle to a specialist repair shop for professional diagnosis and repair.

Codes Related to P1299

• P1288 – Relates to “Cylinder Head Temperature Sensor out of Self-Test Range”
• P1289 – Relates to “Cylinder Head Temperature Sensor Signal Greater Than Self-Test Range”
• P1290 – Relates to “Cylinder Head Temperature Sensor Signal Less Than Self-Test Range”
• P1299 – Relates to “Cylinder Head Temperature Sensor Detected Engine Overheating Condition”

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