|Trouble Code||Fault Location||Probable Cause|
|P1901||Engine Coolant Blower Motor Run-On Relay Short To Positive (AUDI, VOLKSWAGEN) Turbine Shaft Speed Sensor Circuit Intermittent (FORD, LINCOLN, MERCURY) Turbine Shaft Speed Sensor Intermittent (MAZDA) CAN Data Bus Multifunction Control Module 1 (SAAB)|
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What Does Code P1901 Mean?
SPECIAL NOTES: Due to the similar natures of manufacturer specific code P1901 and generic code P0715, non-professional mechanics are strongly urged to familiarize themselves with the basic design and layout of the transmission in the application being worked on, as well as the terminology used by the manufacturer to describe various components of the transmission in that application.
Failing to gain at least a basic understanding of the transmission (and terminology) will almost certainly lead to confusion, misdiagnoses, wasted time, and the unnecessary replacement of parts and components.
In view of the above, it should be noted that manufacturer specific code P1901 – “Turbine Shaft Speed Sensor Circuit Intermittent” as it applies to Ford, Lincoln, Mercury, and Oldsmobile applications, specifically refers to the sensor and circuit that monitors the rotational speed of the transmission turbine shaft, which should not be confused with the transmission output shaft. The transmission output shaft is the final rotating component that leaves the transmission, and it rotates independently of the torque converter.
Moreover, code P1901 and the definition “Turbine Shaft Speed Sensor Circuit Intermittent”, should NOT be confused with generic code P0715 – “Input / turbine speed sensor circuit malfunction”, which code refers to the rotational speed of the torque converter as a unit.
It should further be noted that while generic code P0715 applies to almost all manufacturers, including Ford, Lincoln, Mercury, and Oldsmobile applications, this code refers to the rotational speed of the torque converter in relation to the output speed of the transmission. In practice, this means that there is a significant amount of overlap between generic code P0715, and manufacturer specific code P1901 with regard to probable causes, symptoms, and diagnostic / repair procedures, since torque converter/transmission slippage can set both codes.
Despite this though, there are important distinctions between the two codes; the most important of which is the fact that manufacturer specific code P1901 takes into account the amount of slippage between the two halves of the torque converter, which is generally not the case with generic code P0715. END OF SPECIAL NOTES.
OBD II fault code P1901 is a manufacturer specific code that is defined by car makers Ford, Lincoln, Mercury, and Oldsmobile as “Turbine Shaft Speed Sensor Circuit Intermittent” or sometimes as “Turbine Shaft Speed Sensor Circuit Intermittent/Malfunction. On the above applications, this code is set, and a warning light illuminated when the PCM (Powertrain Control Module) detects an intermittent signal from the TSS (Transmission Turbine Shaft Speed) sensor.
ON applications with automatic transmissions, power (torque) is transmitted from the engine to the transmission by means of a torque converter, which consists of two halves that are not in direct contact with each other. One half of the device is connected directly to the engine, while the other half is driven through viscous forces by means of the transmission fluid that is flung against it by the motion, or rotation of the half that is connected to the engine.
While the above description is an over simplification, it serves to illustrate the basic principles of how power is transmitted from the engine to an automatic transmission. However, because the method of power transmission causes the principal parts of the torque converter to rotate at different speeds, it is necessary to compare the speeds at which the two halves rotate at any given moment in order for the PCM to be able calculate an appropriate shift strategy in conjunction with the transmission control module (TCM).
In practice, most Ford, Lincoln, Mercury, and Oldsmobile applications use two turbine speed sensors. One sensor monitors the rotational speed of the drive side of the torque converter, while a second sensor (which is the sensor code P1901 refers to), monitors the rotational speed of the turbine output shaft specifically. By comparing the two readings, the PCM is able to calculate the total amount of slippage across all the components of the transmission, as well as the amount of torque converter lock-up clutch slippage to allow under some conditions.
In a fully functional system however, the rotational speed of the turbine shaft is only one of the parameters that determines how and when a transmission shifts on the one hand, and how, when, and whether the torque converter lock-up clutch should be applied (or not), on the other. Other typical inputs include data on the engine speed, transmission fluid temperature, throttle position, intake air temperature, engine coolant temperature, manifold absolute pressure, and valid data from the vehicle speed sensor, among others.
From the above it should be obvious that a failure of the turbine shaft speed sensor can have cause serious driveability issues, which is why the PCM sets code P1901 and illuminates a warning light on the first failure cycle on almost all Ford, Lincoln, Mercury, and Oldsmobile applications.
The image below shows a typical turbine shaft speed sensor such as might be found on many Ford applications. However, be aware that the actual appearance and location of the sensor varies greatly between applications, so refer to the manual for the application to identify and locate the correct sensor when diagnosing code P1901.
What are the common causes of code P1901?
Common causes of code P1901 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Defective turbine shaft speed sensor
- Broken, damaged, or fractured reluctor ring
- Excessive clearance between the turbine shaft speed sensor and the reluctor ring. Note that this is a fairly common cause of this code on applications where aftermarket sensors are fitted.
- Failed or failing PCM or other controller, such as the TCM (Transmission Control Module). Note that control module failure is rare and the fault must be sought elsewhere before any control module is replaced
NOTE: Take note that while the PCM is relatively immune to voltage spikes caused by for instance, incorrect jump starting procedures, other controllers such as the transmission control module may not be as immune. Thus, if the fault persists despite several or multiple repair attempts, refer the vehicle to the dealer or other competent repair shop for professional diagnosis with advanced diagnostic equipment that is able to detect programming errors in control modules.
What are the symptoms of code P1901?
Some common symptoms of code P1901 could include the following-
- Stored trouble code, and an illuminated warning light
- Gear shifts may be harsh, erratic, or unpredictable
- Vehicle may enter a failsafe, or limp mode
- In some cases, the engine may stall when the vehicle is stopped
- Cruise control may be deactivated on some applications
- Speedometer may indicate the incorrect road speed, or may not work at all in some cases
How do you troubleshoot code P1901?
NOTE: Take note that on applications that use electromagnetic turbine shaft speed sensors and reluctor rings, it may become necessary to employ an oscilloscope to diagnose some types of issues, such as broken, damaged, or fractured reluctor rings that are located inside the transmission.
Record all fault codes present, as well as all available freeze frame data. This information can be of use in diagnosing some types of intermittent faults.
NOTE: Take note of all additional codes (pending and active) that may be present, and particularly of codes that relate to the transmission fluid temperature, since excessively high fluid temperatures have a direct bearing on the operation of the transmission. If code P1901 is preceded by such codes, be sure to investigate and resolve these codes before attempting a diagnosis of P1901. Failure to do so will almost certainly result in a misdiagnosis and the unnecessary replacement of parts and components.
Refer to the manual for the application to properly locate and identify the correct sensor, as well as the location, color-coding, function, and routing of all associated wiring and connectors. This is an important step since some applications use two turbine shaft speed sensors.
Once the correct sensor and its associated wiring is identified, perform a thorough visual inspection of all wiring and connectors. Look for damaged, burnt, disconnected, shorted, or corroded wiring and/or connectors. Make repairs, or replace wiring as required.
Clear the code after repairs are complete, and operate the vehicle normally before scanning the system again to see if the code returns.
If the code persists but there is no visible damage to wiring, prepare to perform reference voltage (where applicable), ground, continuity, and resistance checks on all associated wiring. Be sure however to disconnect all wiring from the PCM and other affected controllers to prevent damaging any controller during resistance or continuity tests.
Compare all obtained readings with the values stated in the manual, and make repairs or replace wiring as required if deviations from stated values are found. Repeat all checks after repairs are complete to verify that all electrical values fall within the ranges specified by the manufacturer.
Note that since the sensor itself forms part of the control circuit, its internal resistance must be checked as well. Replace the sensor if its measured resistance does not agree with the value specified in the manual, since its resistance is a reasonably good indicator of its overall condition.
NOTE: Do not assume that there is no fault present if initial tests do not immediately reveal a fault. Bear in mind that code P1901 indicates an intermittent fault, which can sometimes be identified by shaking, wiggling, or pulling on all connectors or other connections. Replacing all connectors (or an entire wiring harnesses) that show any signs of corrosion or damage of any kind is often the easiest and quickest way to resolve intermittent faults, regardless of the system that is involved.
If the code persists but electrical values comply with specifications, remove the turbine shaft speed sensor, and inspect it for the presence of metal shavings or particles.
An accumulation of metal particles on a magnetic sensor can seriously affect the operation of that sensor, but more importantly, an excessive accumulation of metal particles indicates serious mechanical trouble inside the transmission. Nonetheless, remove all metal particles from the sensor, reinstall it, clear all codes, and operate the vehicle normally to see if the code returns.
WARNING: Note that on some applications, some transmission fluid may be lost when the turbine shaft speed sensor is removed. Be prepared for this, and be sure to replace all the transmission fluid that is lost in this way to prevent possible damage to the transmission later on.
If the code persists, but all electrical values check out, the resistance of the turbine shaft speed sensor conforms to the manufacturers’ specifications, there is no damage to wiring, and all connectors/connections are known to be secure, suspect either a faulty PCM or a defective reluctor ring.
However, since PCM failure is rare, a defective reluctor ring is the more likely cause but in many cases, the reluctor ring is not accessible, and gaining access to it may require the removal and disassembly of the transmission. If a defective reluctor ring is suspected, the wiser option would be to refer the vehicle to the dealer, or other competent repair shop for professional diagnosis and repair.
Codes Related to P1901
There are no known manufacturer specific codes that are directly related to P1901.
Other Manufacturer Specific Definitions for P1901Turbine Shaft Speed Sensor Circuit Intermittent (Ford)
Engine coolant blower motor run-on relay - short to positive (Volkswagen)
Engine coolant blower motor run-on relay - short to positive (Audi)
Engine oil pressure sensor range/performance (Dodge)
Engine oil pressure sensor range/performance (Freightliner)
Turbine shaft speed (TSS) sensor -circuit intermittent (Lincoln)
Turbine shaft speed (TSS) sensor- intermittent (Mazda)
Turbine shaft speed (TSS) sensor -circuitintermittent (Mercury)
CAN data bus, multifunction control module 1 (Saab)