|Trouble Code||Fault Location||Probable Cause|
|P1412||EGR Differential Pressure Sensor Signal Too Low (AUDI, VOLKSWAGEN)
EGR Valve Pintle Frozen (MAZDA)
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What Does Code P1412 Mean?
Special note on trouble code P1412 and Land Rover vehicles: While DTC P1412 is a manufacturer-specific code that may affect several OBD II compliant vehicles, the causes and symptoms of this code typically vary between most vehicle makes. This article will therefore deal with code P1412 as it applies specifically to Land Rover vehicles.
OBD II fault code P1412 is a manufacturer-specific trouble code that is defined by carmaker(s) Land Rover as “Secondary Air Injection System Fault Bank 1”, or, sometimes as “Secondary air injection (AIR) system, malfunction”, and is set when the PCM (Powertrain Control Module) detects a failure or malfunction in the secondary air injection system on Bank 1. Note that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.
The purpose of secondary air injection systems is to supply additional oxygen (in ambient air) to the exhaust stream to facilitate improved combustion of unburned hydrocarbons (unburned fuel) in the catalytic converter to convert harmful exhaust emissions into innocuous substances like carbon dioxide and water vapor.
If gasoline engines and their control/management systems were perfect, the air/fuel mixtures these engines burn would always be at a perfectly stoichiometric ratio, regardless of operating conditions, or the engine speed and load. However, while most modern engine and fuel management systems are capable of establishing fuel-to-air ratios of 14.7 parts of air to one part of fuel for some of the time, and maintain ratios that come close to stoichiometric for most of the time, no engine and fuel management system in use today can maintain perfect stoichiometric air/fuel ratios all of the time.
Moreover, one of the defining characteristics of gasoline combustion is that the process is relatively difficult to achieve and sustain in cold engines, and during cold start-ups, engine management systems typically enrich the mixture by adding fuel to assist with combustion. While this helps to improve combustion in cold engines, it has the undesirable effect of producing relatively large amounts of unburned fuel to enter the exhaust system until the engine warms up sufficiently to obviate the need for additional fuel in the air/fuel mixture.
On older vehicles that were fitted with early iterations of catalytic converters, the highly enriched exhaust stream passed through the converters unconverted, until the heat of the exhaust stream heated the catalysts in the converter sufficiently for the conversion of hydrocarbons into harmless substances could begin. The required temperature is typically above 5500F, and on some older exhaust after treatment designs, it could take several minutes for a catalytic converter to become hot enough to initiate and sustain the conversion process.
Therefore, in practice, older vehicles emitted up to 80% of their total emissions during a trip in the time it took for their engines to warm up and to address this problem, vehicle manufacturers developed ways to inject additional air into the exhaust system. The objective was to add additional air to the exhaust stream to increase its temperature, which dramatically reduced catalytic converter warm-up times, and by extension, the volume of harmful emissions emitted by cold engines.
These systems became known as “secondary air injection systems” and early iterations used belt-driven air pumps to inject pressurized air into the exhaust system. Modern systems, however, use input data from various engine sensors such as the coolant temperature sensor, engine speed sensor, vehicle speed sensor, as well as exhaust temperature and exhaust backpressure sensors to calculate the amount of additional that is required.
As a practical matter, modern secondary injection systems are electronically controlled, in the sense that the PCM uses input data from several sensors to control and manage the air pump and a variety of valves that make up the secondary air injection system. Depending on both operating conditions and environmental factors such as ambient temperatures, the PCM will a) activate the air pump only when required, and b), it will deactivate the pump and isolate the secondary injection system from the exhaust system to prevent hot exhaust gas from damaging the pump when the pump is deactivated.
In terms of practicalities, the PCM will monitor the operation of the catalytic converter via the oxygen sensor downstream of the converter, and when it detects that the converter has started the conversion of exhaust gas, it will deactivate the secondary air injection system. It is perhaps worth noting that while early secondary air injection systems typically operated for about 100 seconds (and sometimes, for longer) the combination of heated oxygen sensors, advanced, three-way catalytic converters, and improved engine/combustion chamber designs has reduced typical secondary air injection duty cycles to about 10 – 12 seconds.
On all vehicles that are fitted with secondary injection systems, these systems are integral parts of the overall engine and fuel management system, so when the PCM detects failures, defects, or malfunctions in the secondary air injection system, it will recognize that it cannot control or manage the emission control system effectively. When this happens, the PCM will set code P1412, and illuminate a warning light.
Where is the P1412 sensor located?
This image shows the location (circles and arrowed) of the secondary air injection pump and some associated tubing on Series II Discovery and some P38 Range Rover models.
Note that on other Land Rover applications, the appearance and location of the secondary air injection pump and associated components may be different from the example shown here. Therefore, it is highly recommended that you consult reliable service information for the affected application to locate and identify parts and components correctly. Note, also, that on some applications, it may be necessary to remove and/or disassemble unrelated engine parts/components to gain access to defective or suspect secondary air injection system components.
What are the common causes of code P1412?
Typical causes of code P1412 on Land Rover vehicles could include one or more of the following-
- Defective, failed, or malfunctioning air pump (Most common)
- Defective, failed, or malfunctioning valves in the secondary air injection system
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Defects in, or failures of any implicated sensor
- Exhaust leaks
- Clogged or leaking feed lines connecting the air injection system to the exhaust system
- Failed or defective oxygen sensors, but note that this will typically be indicated by dedicated oxygen sensor codes
- Failed, damaged, clogged, or otherwise unserviceable catalytic converter
- Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is reprogrammed or replaced
What are the symptoms of code P1412?
Common symptoms of code P1412 could include the following, but note that it is exceedingly rare for this code to produce significant or even discernible driveability issues-
- Stored trouble code and an illuminated warning light
- In some cases, and depending on the nature of the problem, one or more additional codes relating to one or more implicated sensors may be present along with P1412
- In some cases, failing and/or damaged air injection pumps may emit whining, grinding, or whistling noises
- One or more readiness monitors may not initiate, or may not run to completion
- The vehicle will fail an emissions test
Other Manufacturer Specific Definitions for P1412EGR Differential Pressure Sensor Signal Too Low (Volkswagen)
EGR Differential Pressure Sensor Signal Too Low (Audi)
Secondary air injection (AIR) system, bank 1 – malfunction (Land Rover)
Exhaust gas recirculation (EGR) solenoid – malfunction (Mazda)