Symptoms and Severity of the Code
After the second key cycle, the PCM/TCM will illuminate the check engine light and force the transmission into “limp-home” or “safe-mode.” There will be an obvious loss of power, more noticeable when taking off from complete stops. In this mode, the transmission starts in third gear, which is hard on the internal clutches of the transmission.
From my experience, this can cause serious internal damage to the transmission, so it should be fixed as soon as possible. Avoid using the vehicle until repairs can be made.
Causes
Potential causes for setting this code are as follows:
- Faulty transmission range sensor “B”
- Faulty “B” wiring
- (Rarely) Faulty PCM or TCM
Diagnostic and Repair Procedures
The transmission range sensor receives a 12-volt signal from the ignition switch and then sends a 12-volt signal, on the appropriate circuit based on the gear position, to the PCM/TCM.
P2804 is set when the signal is missing at the PCM/TCM. A scan tool with the ability to read live data is the most accurate way to diagnose this DTC, but if it is not available, here are some things that can be checked with a digital volt-ohmmeter (DVOM). From my experience, the most common cause of intermittent signal issues is related to wiring.
In this case, a close visual inspection of the sensor range wiring harness and the internal contacts of the range sensor connector should be done first and thoroughly. If anything is found suspicious during the inspection, repair the issue, clear the codes, and test the vehicle. If the DTC returns, set the DVOM to volts and probe the appropriate circuits at the PCM/TCM and “wiggle” the harness at and leading to the range sensor. If no intermittent voltage loss is visible on the multimeter, suspect a faulty range sensor.
Related transmission range sensor codes: P2800, P2801, P2802, and P2803.