SPECIAL NOTES: While manufacturer specific OBD II code B2799 is extremely common on Toyota and GM applications, the code has vastly different definitions since they refer to different issues on GM and Toyota applications. Therefore, this article will describe code B2799 as it applies to both Toyota and GM applications, but to avoid confusion, each description will be separated by proper headings within the same field or section. END OF SPECIAL NOTES.
OBD II fault code B2799 is a manufacturer specific code that is defined by carmaker Toyota as “Engine Immobilizer System Malfunction”, and is set when the PCM (Powertrain Control Module) detects either a communication error between itself and the transponder key, or a malfunction in one or more communication lines between itself, the transponder key, and the immobilizer control module. Note that this code can also be set when one or more implicated control modules detect incorrect security codes being transmitted from the key to the PCM or immobilizer control module.
Modern automotive security/anti-theft systems are highly complex systems that depend on the transmission and receipt of extensive strings of security codes, and in practice, the key, immobilizer control module, and the PCM all contain the same codes in the same configuration. Note also that on some Toyota applications, the same codes are programmed into the central locking system, meaning that only the correct key can lock/unlock the vehicle remotely using the key fob.
In terms of operating principles, the immobilizer control module is connected to a receiver that fits around the ignition lock, and when the key is inserted into the ignition lock, the receiver “reads” the security information that is programmed into a chip in the key. This information is amplified to increase accuracy, and then relayed to the immobilizer control module, which compares its own programming with that received from the key. Only if all the transmitted and received security codes match, will the immobilizer enable the fuel and ignition systems to allow the engine to start.
While the above description is admittedly a gross over simplification of an extremely complex system of checks and verifications, it will nevertheless suffice to illustrate the point that unless all the pre-programmed security codes and other vehicle identifying information contained in the key, PCM, and immobilizer control module match exactly, the immobilizer will not allow the engine to start. In some cases though, the engine may start but will be shut down by the immobilizer after about two seconds.
OBD II fault code B2799 is a manufacturer specific code that is defined by carmaker General Motors as “Suspension Control Select Switch Circuit Open”, and is set on General Motors applications when the PCM (Powertrain Control Module) and/or BCM (Body Control Module) detects a failure, defect, or malfunction either in the suspension control switch, or in wiring that is associated with the suspension control system.
NOTE: Be aware that this code does not apply to issues with the more advanced Speed Sensitive Suspension Control System, which uses the vehicles’ road speed to adjust the characteristics of the vehicle’s suspension automatically.
On systems that use manually selectable suspension control, a driver has a choice between two shock damping levels. Selecting a specific level involves activating a switch, which feeds power to solenoids that are contained within the shock absorbers.
Normal shock absorbers work on the principle of fluid resistance, which involves allowing a fluid, (in this case, oil) to pass through a small orifice in the shock absorbers’ piston as it moves through the oil charge in the shock absorbers’ tube. If the movement is slow, the oil passes through the orifice easily, but at higher rates of movement, the oil can only pass through the orifice at the rate that is dictated by the oil’s viscosity. The practical effect of this is that when the shock absorbers’ piston moves though the oil slowly, shock damping is decreased because the oil moves though the orifice relatively easily.
Conversely, if the piston moves through the oil at a high rate of speed, the oil cannot pass through the oil as easily, mainly because its viscosity prevents fast movement through the orifice. Therefore, shock damping is increased, which has the practical effect of resisting both body roll movements, and large oscillations of the suspension.
However, with selectable shock damping, the diameter of the orifice in the shock absorbers’ piston can be adjusted with a solenoid, which means that the rate of oil-flow through the piston can be controlled to suit current driving conditions. Note though that the vehicle’s ride height is not affected; all that changes is the level of shock damping when the selector switch is manipulated.
When the PCM detects a fault (an open circuit, in the case of code B2799) in the suspension control system, it will set code B2799, and set a warning light as a result.
