P2804 Transmission Range Sensor “B” Circuit Intermittent
OBD-II Trouble Code Technical Description
Transmission Range Sensor "B" Circuit High
What does that mean?
This is a generic powertrain code, which means it covers all makes/models, 1996-newer. However, specific troubleshooting steps will vary depending on the vehicle.
This is a generic powertrain diagnostic trouble code (DTC) in the transmission sub-group. It is a type "B" code meaning that the powertrain control module (PCM) or the transmission control module (TCM) will not turn on the check engine light unless the conditions to set the code are present for two consecutive key cycles. (key on-off, off-on)
The PCM/TCM uses the transmission range sensor, sometimes called the inhibitor switch, to identify which gear position the shift lever is in. The code definition itself explains the problem that is causing the code; the signal from the range sensor is not present all of the time, or it is intermittently missing.
Example of an external Transmission Range Sensor (TRS):
TRS image from Dorman
Symptoms & Severity of Code
After the second key cycle, the PCM/TCM will turn on the check engine light and force the transmission into "Limp-home" or "safe-mode". There will be an obvious power loss, most noticeable when taking off from complete stops. When in this mode, the transmission starts off in third gear which is hard on the internal clutches in the transmission.
In my experience this can cause severe internal damage to the transmission so it should be corrected as soon as possible. Avoid using the vehicle until repairs can be made.
Causes
Potential causes for this code to set are:
Diagnostic and Repair Procedures
The transmission range sensor receives a 12 volt signal from the ignition switch then it sends a 12 volt signal, on the appropriate circuit according gear position, to the PCM/TCM.
P2804 set when the signal is missing at the PCM/TCM. A scan tool that has the ability to read live data is the most accurate way to diagnose this DTC, but if one is not available here are a couple of things that can be checked with a digital volt ohm meter. (DVOM) In my experience the most common cause of intermittent signal issues are wiring related.
In this case, a close visual inspection of the range sensor wiring harness and the internal contacts of the range sensor connector should be performed first and thoroughly. If anything is found suspect during the inspection, repair the issue, clear the codes and test drive the vehicle. If the DTC returns, set the DVOM to volts and back probe the appropriate circuits at the PCM/TCM and "wiggle" the harness at and leading to the range sensor. If no intermittent voltage loss can be seen on the meter suspect a faulty range sensor.
Related Transmission Range Sensor codes: P2800, P2801, P2802, and P2803.
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"Delete Error Code Permanently, Disable DTC Error Code Function for p2804 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p2804 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p2804.
