|Code||Fault Location||Probable Cause|
|P0869|| Transmission fluid pressure (TFP) sensor -high |
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|Wiring, short to positive, TFP sensor, ECM/PCM/TCM|
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What Does Code P0869 Mean?
SPECIAL NOTES: When diagnosing code P0869 –“Transmission fluid pressure (TFP) sensor –high”, non-professional mechanics are limited to a few basic, generic steps that may or may not resolve the issue. Diagnosing this code accurately beyond the basic steps outlined here almost always requires advanced diagnostic equipment such as transmission simulators (and sometimes oscilloscopes), above average diagnostic skills in general, and expert-level knowledge of automatic transmissions and their control systems, in particular.
Therefore, the information presented here is intended for general informational purposes only, and should NOT be used in ANY diagnostic/repair procedure for this code on ANY application without making proper reference to the manual for the affected application. Non-professional mechanics are strongly urged NOT to continue the diagnostic steps beyond what is presented here; doing so could cause irreparable damage to the transmission as well as the entire electrical system of the application. END OF SPECIAL NOTES.
OBD II fault code P0869 is a generic code that is defined as “Transmission fluid pressure (TFP) sensor –high”, and is set when the PCM (Powertrain Control Module) detects a significant difference between the actual transmission line pressure, and the desired transmission line pressure.
In the context of code P0869, “transmission fluid pressure” refers to transmission line pressure, which is the pressure that holds various components in place when a particular gear is selected. However, this pressure is not constant across all gears; the desired pressure for a particular gear is calculated by the Transmission Control System, using measured engine torque as the primary input data, which is supported by input data from various engine and transmission sensors. Pressure variation and regulation is accomplished by varying the duty cycle of the Pressure Control Solenoid.
Typically, a 5% duty cycle means the pressure control solenoid is “OFF”, resulting in maximum allowable line pressure, while a duty cycle of around 62% or so means the pressure control solenoid is “ON”, resulting in the minimum allowable line pressure.
In practice, the transmission line pressure is set to a predefined range. Note that this base pressure differs between applications, but whatever it is set to, it is set to remain within that range both during gear shifts, as well as when the transmission is in either “P” or “N” to ensure smooth and consistent operation in all gears. In a fully functional transmission, the actual pressure is both continuously monitored by a dedicated line pressure sensor, and compared to the desired pressure.
Thus, should the PCM detect that the actual line pressure is exceeding the highest pressure ever recorded while a particular (forward) gear is selected and the pressure control solenoid duty cycle is set at or close to its maximum value (resulting in the minimum allowable line pressure),it will set code P0869, and may also illuminate a warning light.
What are the common causes of code P0869?
Some common causes of code P0869 could include the following-
- Defective pressure control sensor
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Mechanical failure of transmission components
- Failed or failing PCM or TCM. Note that this is a rare event, and the fault must be sought elsewhere before any control module is replaced.
What are the symptoms of code P0869?
Some common symptoms of code P0869 could include the following-
- Stored trouble code and an illuminated warning light
- Additional transmission related codes may be present
- Transmission may overheat
- Varying degrees of transmission slippage may be present
- One or more (or all) gears may not engage
- In some cases, the transmission may enter a fail-safe or “limp mode”
How do you troubleshoot code P0869?
NOTE: Take note that if the transmission had become noisy at about the same time code P0869 appeared the transmission had already suffered severe mechanical damage, and trying to resolve this code at this point is a waste of time and money. If the transmission is noisy the only viable option is to replace the transmission.
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.
Refer to the manual to locate the pressure control harness, but be sure to determine the color coding and function of each wire in the harness to avoid testing the wrong circuit.
Perform a thorough visual inspection of all associated wiring and connectors, and look for damaged, burnt, shorted, disconnected, or corroded wiring and connectors. Make repairs as required if damage is found.
If the wiring is free of damage, prepare to perform resistance, continuity, ground, and where applicable, reference voltage checks on all wiring, but be sure to disconnect the wiring from all relevant control modules to prevent damaging the controllers during this step.
Compare all obtained readings with the values stated in the manual, and repair or replace wiring as required to ensure that all electrical values fall within the ranges specified by the manufacturer.
NOTE #1: Pay particular attention to the internal resistance of both the pressure control solenoid, and the line pressure sensor since resistance is a reasonably good indicator of their overall condition. However, do not condemn the pressure control solenoid until the transmission’s internal wiring had been checked and is known to be in perfect condition, but replace the pressure sensor with an OEM replacement if its resistance does not agree with specified values.
NOTE #2: In addition, bear in mind that if the transmission’s internal wiring is defective, the entire internal harness must be replaced to prevent issues with short circuits later on.
Take note that if the fault persists beyond Step 3, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair. From this point on, if all electrical values agree with specified values/ranges, the operation of the transmission has to be simulated and the results analyzed using high-tech diagnostic equipment in order to arrive at an accurate diagnosis.