|Trouble Code||Fault Location||Probable Cause|
|P1121||Electric Throttle Control Actuator (Infiniti, Nissan) Throttle Position (TP) Sensor Circuit Intermittent High Voltage (Buick, Cadillac, Chevrolet, GM, Pontiac, Saturn, Suzuki) Throttle Position Sensor Inconsistent with Mass Air Flow Sensor (Ford, Lincoln, Mazda, Mercury)|
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What Does Code P1121 Mean?
SPECIAL NOTES: Although this guide will deal with code P1121 – “Electric Throttle Control Actuator”, as it pertains to Nissan and Infiniti applications, be aware that some sources also list code P1121 as “Throttle Position Sensor [TPS] Circuit Intermittent High Voltage”, on some imported models. Take note that this definition describes wiring issues in the TPS (Throttle Position Sensor) control circuit, and as such, this particular definition has no bearing on code P1221 where it is defined as “Electric Throttle Control Actuator”. Refer to the Troubleshooting section of this guide for more information regarding the possible failures of the throttle actuator that can be indicated by P1121 – “Electric Throttle Control Actuator”.
Wiring issues (apart from damaged wiring) that cause abnormal reference or signal voltages rarely feature in instances of P1121- “Electric Throttle Control Actuator”, so always consult the manual for the application being worked on for detailed information on code P1121 as it pertains to that particular application to avoid misdiagnoses, and the unnecessary replacement of parts and components. END OF SPECIAL NOTES:
OBD II fault code P1121 is a manufacturer specific code that is defined by carmaker Nissan, and by extension, Infiniti, as “Electric Throttle Control Actuator”, or sometimes as “P1121 – Throttle Motor Malfunction”, depending on the model year. On applications that use either definition, code P1121 is set when the PCM (Powertrain Control Module detects a failure of, or malfunction in, the throttle body which incorporates a stepper motor, a throttle position sensor, a return spring and the throttle plate itself.
In terms of operation, the PCM uses input data from the Accelerator (Throttle) Pedal Position Sensor and several engine sensors to calculate a throttle opening that suits current operating conditions, based on the current engine speed and load. Based on input data received, and assuming that all relevant sensors and control circuits work as intended, the PCM generates a signal that activates the stepper motor in the throttle body to either open or close the throttle plate, thereby establishing effective throttle control.
When the desired throttle opening deviates from the actual throttle opening as measured by the integrated Throttle Position Sensor by more than an amount set by the manufacturer for that particular application, the PCM sets code P1121, and illuminates a warning light. In some cases, such as when the throttle plate sticks in the open position, the PCM may also initiate a “Fail Safe” or “Limp Mode” when code P1121 sets, in which case the automatic transmission may be prevented from shifting, and driver has no, or very limited throttle control.
The image below shows a typical Nissan electronic throttle control actuator. Note that due the construction of the unit (which is typical for Nissan/Infinity applications) water and moisture can easily enter the mechanism: in fact, damage caused by water and moisture ingress as shown here, is one of the most common reasons why these components fail on many Nissan/Infiniti applications.
What are the common causes of code P1121?
The most common causes of code P1121 are much the same across all applications, and these could include the following-
- Broken, binding, or sticking return spring
- Corrosion of internal components
- Mechanical failure of internal components
- Mechanical wear of internal components
- Damaged, burnt, shorted, disconnected, or corroded wiring and connectors. Note however that these conditions will almost always be indicated by codes other than P1121
- Failed, or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced
What are the symptoms of code P1121?
The typical symptoms of the code are largely determined by the malfunction concerned, but these could include the following-
- Stored trouble code and an illuminated warning light
- Idling speed that falls outside of the acceptable range (high or low)
- Engine idle may be rough or erratic if the idling speed is too low
- Engine may stall when a gear is selected (automatic transmission) if the idling sped is too low
- Gear selection may be harsh when “D” or “R” is selected if the idling speed is too high
- Vehicle may be difficult to control when stopping while a gear is selected if the idling speed is too high
- Throttle response may be poor if the throttle plate opening is out of range
- Vehicle may enter limp mode when “Malfunction C” occurs.
How do you troubleshoot code P1121?
SPECIAL NOTES: As stated elsewhere, code P1121 – “Electric Throttle Control Actuator” is hardly ever caused by wiring issues, but having said that, it can never hurt to inspect the throttle actuator’s control circuit to eliminate any possible wiring issues that could conceivably have contributed to setting the code. Note however that wiring issues will almost certainly be indicated by codes other than P1121, but in some cases, certain types of electrical/wiring problems may still be in the “code pending” stage, so be sure to check for pending codes in all instances of code P1121 – “Electric Throttle Control Actuator”.
In the event that other codes (pending or active) present but a thorough visual inspection of all associated wiring and connectors does not reveal obvious signs of damage, short circuits, or other issues, find the section in the manual for the application being worked on that deals with the throttle control actuators’ control circuit, and follow the directions provided EXACTLY to test all wiring for problems relating to continuity, abnormal resistances/reference voltages, and ground connectivity. Make repairs as required, and retest the system to verify that all electrical values fall within the manufacturer’s specifications. END OF SPECIAL NOTES.
Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on. Note however that with this code, “intermittent faults” usually refer to intermittent faults in the stepper motor windings and/or connections, or sometimes to an intermittent loss of electrical contact in the connector that connects the throttle actuator to the wiring harness.
Once it is certain that the throttle actuator’s electrical connector is in good working order, there are only three other possible failures to consider. Note the order in which they are listed here- this is important, since the first two must be resolved or eliminated as the cause for the code before the third can be diagnosed and repaired.
- Malfunction A – Electric throttle control actuator does not function properly-
In Nissan-speak, this means that the return spring may be broken, sticking, or is not closing the throttle plate at the correct rate for that application.
- Malfunction B – Throttle valve opening angle is not within the specified range-
This means that the actual, measured position of the throttle plate does not agree with the target, or desired angle of opening the throttle plates needs to be at to suit any given engine speed and load. This can be caused by Malfunction A, and it can affect the engine at any speed throughout its operating range.
- Malfunction C – ECM detects that the throttle valve is stuck in the “open” position-
This condition is self-explanatory, but the results of the condition can be dramatic. To protect both the engine and the vehicles’ occupants against the effects of losing throttle control, the PCM will assume control of the transmission to prevent gearshifts, and cut the fuel supply to shut the engine down. Moreover, while the PCM will allow the engine to restart in most cases, it will initiate a “Fail Safe”, or “limp mode”, during which the engine speed will be limited to about 2 000 RPM, or sometimes less, and the driver will be deprived of throttle control. The transmission may also be prevented from shifting beyond first or second gear.
Nissan throttle actuators are not known for their reliability or durability, and many mechanics will simply replace the actuator with an OEM part to resolve the code. However, this is an expensive option that is not always available to all, so non-professional mechanics that are on a budget could proceed as follows to diagnose the code in this order –
“Malfunction A” – Electric throttle control actuator does not function properly- If the code reader or scanner has control functions, clear the code and use the scanner to command the actuator fully open from the fully closed position several times to see if an intermittent fault is present. The angles of opening will usually be displayed in degrees on most scanners, so note the minimum and maximum values, and compare these to the values specified in the manual.
If the return spring is defective, or impeding the movement of the throttle plate in some way (such as preventing the throttle plate from opening or closing fully within the time specified by the manufacturer), this will almost certainly be indicated by the closure rate of the throttle plate, which will also be displayed on most scanners.
Apply a good quality spray-on lubricant to the spring and throttle plate spindle, and repeat the test several times to see if the displayed readings change in any way. If the readings change in a positive way, the fault may be resolved, but be aware that in some cases, it may be necessary to dismantle the actuator to ensure that the lubricant reaches all point on the spring and spindle. If disassembly of the actuator is required, be sure to follow the directions in the manual exactly to prevent damaging anything else.
NOTE #1: Of course, if the return spring is broken, this will be immediately apparent. In this case, the better option is to replace the entire assembly with an OEM part, since rebuild kits rarely offer the performance or durability of OEM parts.
NOTE #2: If a scanner with control functions is not available, the only remedy is to remove the actuator from the engine, and to strip it down to inspect all internal parts visually for signs of damage, corrosion, or mechanical failure.
“Malfunction B” – Throttle valve opening angle is not within the specified range- is just as often caused by mechanical wear of the actuator’s internal components, as it is caused by carbon or other deposits that prevent the throttle plate from closing all the way- or at least to the point where its degree of opening regulates the engine’s idle speed.
Thus, if the engine idling speed is too high or too low, the throttle plate is almost certainly not closing to the position the PCM expects it to be at, or mechanical wear in the gears that drive the throttle plate is worn to the point where the throttle plate close too far, which starves the engine of air and fuel.
In the first case, a simple cleaning of the throttle body bore with an approved solvent will resolve the problem nine times out of every ten. Note that in some cases, repeat applications of the solvent might be required to remove stubborn deposits.
In the latter case where mechanical wear is involved, the problem might be resolved by performing both the “Idle Air Relearning” and the “Throttle Valve Closed Position Learning” procedures, but note that whether this works or not is largely determined by the amount of wear in the mechanism. Perform the idle relearning procedure in strict accordance with the instructions provided in the manual, but note that if the procedure does not produce positive results after several attempts, it is likely that neither procedure can compensate for the amount of wear in the mechanism. If this is suspected to be the case, the only reliable remedy is replacement of the actuator assembly with an OEM part.
NOTE: The “Idle Air Relearning” and “Throttle Valve Closed Position Learning” procedures are different for different applications, and sometimes even between models in any given model range. For this reason, it is critically important that only the procedure prescribed in the manual for the application being worked should be followed, since getting this step wrong can lead to hours of wasted time, loads of frustration, and in some cases, the unnecessary replacement of a hugely expensive component.
“Malfunction C” – ECM detects that the throttle valve is stuck in the “open” position- is almost always caused by a mechanical failure of one or more internal components of the throttle actuator, or the presence of corrosion that can cause moving parts to suddenly stick or bind while the throttle is open.
The only reliable remedy for either condition is to replace the unserviceable throttle actuator with an OEM replacement, and if the problem was caused by corrosion, to take suitable measures to ensure that water or moisture does not enter the mechanism again. One way to do this is to seal the outside joint between the plastic and metal parts of the assembly with a suitable sealer, but avoid the use of silicone-based sealants, since the acetic acid in these compounds is known to attack aluminum. Use RTV-grade gasket making compounds instead.
NOTE #1: Be sure to follow the instructions in the manual exactly when removing the throttle actuator from the inlet ducting to avoid damaging other components. Also, never re-use any gaskets, or use gasket sealer on new gaskets when refitting a replacement actuator. Re-using old gaskets often cause vacuum leaks that can seriously affect the engine’s operation, while many gaskets sealers can affect the sealing properties of gaskets that are made from some oil/gasoline-resistant gasket materials.
NOTE #2: While rebuild kits (that sometimes include a replacement stepper motor) are widely available, rebuilding a safety-critical component like a throttle actuator, or replacing a broken unit with a rebuilt replacement is NOT recommended. There is often no telling where the replacement parts were made, which means that warranties in respect of rebuilt parts and units are often worse than useless- not to mention the fact that an engine entering limp mode on a busy freeway during rush hour traffic is not the right time to discover that a throttle actuator was rebuilt with substandard parts.
Codes Related to P1121
Note that code P1121 – “Electric Throttle Control Actuator” refers specifically with the actual throttle control actuator, and as such, all known related codes refer to failures, malfunctions, or defects in parts, components, or circuits that are closely related to the throttle actuator, but do not include failures or malfunctions of the throttle actuator itself. Always refer to the manual for the application being worked on for detailed information on codes that affect parts/components/circuits such as the Throttle Pedal Position Sensor, Secondary Throttle Position Sensor, Idle Speed Sensor/Control, and others that could possibly affect the operation of the Throttle Control Actuator.
Other Manufacturer Specific Definitions for P1121Throttle Position Sensor Inconsistent with Mass Air Flow Sensor (Ford)
Throttle Position Sensor Circuit Intermittent High Voltage (GM)
Accelerator pedal position (APP) sensor - range/performance problem (Toyota)
Heated oxygen sensor (HO2S) heater short to ground (Volkswagen)
Throttle position (TP) sensor - circuit/ intermittent voltage high (Acura)
Heated oxygen sensor (HO2S) 2, Bank 2 - heater short to ground (Audi)
Switching Solenoid for Air Assisted Injection Valves Bank 2 Control Circuit Signal High (BMW)
Throttle position (TP) sensor -circuit malfunction -voltage high (Buick)
Throttle position (TP) sensor -circuit malfunction -voltage high (Cadillac)
Throttle position (TP) sensor -voltage high, intermittent (Chevrolet)
Decreased Engine Performance Due To High Intake Air Temp (Dodge)
Throttle position (TP) sensor – position lower than expected (Honda)
Throttle Position Input - Abnormal (Hyundai)
Throttle motor – malfunction (Infiniti)
Throttle position (TP) sensor – circuit/ intermittent voltage high (Isuzu)
AT- TP sensor signal (Kia)
Throttle position (TP) sensor – range/ performance problem (Land Rover)
Accelerator pedal position (APP) sensor – range/performance problem (Lexus)
Throttle position (TP) sensor -inconsistent with mass air flow (MAF) sensor signal (Lincoln)
Throttle position (TP) sensor – incomparable with MAF sensor signal (Mazda)
Throttle position (TP) sensor inconsistent with mass air flow (MAF) sensor signal (Mercury)
Pedal Position 1 Range/Performance Problem (Mini)
Throttle valve position motor – malfunction (Nissan)
Throttle position (TP) sensor -circuit malfunction -voltage high (Oldsmobile)
Throttle position (TP) sensor -voltage high,intermittent (Pontiac)
Park/neutral position (PNP) switch/neutral position (NP) switch – voltage low (Saab)
Throttle position (TP) sensor, circuit malfunction,voltage high (Saturn)
Park/neutral position (PNP) switch/neutral position (NP) switch – voltage low (Subaru)
Throttle Position Sensor Intermittent High Voltage (Suzuki)
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