QuestionHello,
I'm having a problem with my car...It runs good but sometimes when I'm driving all of a sudden the fuel gauge drops to empty than the other gauges also drop to 0, the airbag, check engine, ABS lights turn on. When this happens also in the odometer I get a NO BUS message! oh also the air conditioner turns on by itself...I have some codes that I got by following some steps from your website....the codes I get are P1684, P1687, and P1686. In some occasions this happens about 5 times in one day! I would truly appreciated if someone would help me figure it what is wrong with the car!
Thank You
AnswerHi Vernice,
The issues have to do with the digital communication system that interconnects the engine control computer, transmission control computer, body computer, instrument cluster/warning lights, AC/heater, sentry key immobolizer (prevents theft by requiring a programmed key to operate the ignition switch), etc. There are several possible reasons: one of those units I listed could be intermittently defective or the 2 wires that connect them (called the "bus") may have some loose connections at one of the units. It would be much less expensive if it were the latter rather than the former.
Because the problem manifests itself mainly at the instrument cluster (so far the car runs fine, correct?) my inclination would be to focus on the bus connections to the instrument cluster. It is not difficult to remove the cluster (let me know if whoever wants to do it would like the instruction about how to), and once that is unplugged my suggestion would be to reheat the solder joint on the pin #5 of the green plug's socket where it connects to the circuit board. That is the wire that carries the bus messages into the cluster. Those solder joints are a common place of failure. It only requires a pencil-type soldering gun. This task could be done at a speedometer repair shop if you are in a city which is large enough to support such a business. Otherwise, any shop that does electrical repair on the instrument cluster and was competent/conscientious could give it a try. They could prophylactically reheat the other 19 joints while they were there doing pin 5, it just takes a few seconds to do each.
I would choose to have the dealer do it only as a fallback because I suspect they might try to get you to agree to replaces the cluster or one of the other components of the system like the engine computer all of which are quite expensive.
See if re-soldering solves both the loss of function of the cluster and the spontaneous AC startup issue.
The 1684 code says that the battery supply to the engine computer was disconnected sometime in the past 50-100 times that the car was started. If you haven't had any work done on the car in that time period then I would check to make sure the battery clamps are tight on the battery posts (that could explain everything!). The 1687 says what you already know ('no bus' message at cluster) and the 1686 says the communication over the bus to the security key system (assuming that you do have the type of ignition key that has the colored tab on it) was also interrupted. If you have had no problem starting the car and getting it to 'catch' then I would set that code aside for now.
That is my best advice.
Roland
PS I would appreciate knowing how this repair goes with you.
