After driving my 1994 Camry 4cl for about 30 minutes the speedometer drops to 0 then spikes and jiggles on applying the brakes. Letting off of the brakes the speedometer returns to normal. Continuing to drive around town the problem worsens such that the transmission seemed to go to neutral as the engine revved with no forward thrust. After the engine cools, I can again drive without problems for about 30-40 minutes. Took in to my mechanic and he said he needed to change the distributor and the speed sensor for about $800.00. I changed out the distributor myself with no improvement. Unwilling to try the speed sensor without some feed back. Any help?

 

Determine if the braking action on the car triggers the speedo issue. Or applying the brake only to the extent the brake light switch closes, making the issue a possible wiring problem.

Is engine revving and lack of forward thrust linked to the speedo problems, or has speedo problem resolved themselves but engine still revs.

Transmission shifting is electronic and based in part on signals from the speed sensor.

When revving with no forward thrust, if MPH is low enough try downshifting. This will manually shift gears.

 

I had a similar problem with a 95 accord and it was the speed sensor. Do as Joey suggests though to rule things out.

 

Thanks for the responses. Just drove the car on freeway for about 1 1/2 hours at 70 mph with no issues. Upon arriving at my destination first couple of stops were normal, then at about 40 mph upon tapping the brakes the speedo dropped to 0 then immediately returned to normal speed while the brakes were still being applied. This happened at each stop when I was at least at 40 mph. Under 40 there was no drop or spike. This trip I did not lose power and the transmission did not disengage. I did clean the oil that had collected around the speed sensor on the transmission and tried to clean out the harness. Not sure if my braking was light enough as you asked, will check that out tomorrow when I return home. When the problem originally surfaced, I was able to continue driving by manually downshifting as you suggested.

 

If possible try the following. Find the brake light switch under dash. Follow the brake peddle arm to switch. Connect wires to switch electrical terminals to allowing activating brake lights by connecting the two wires without actually applying brakes. Then go drive add at times connect the wires.

It may be when the brake light switch is activated the problem happens, not the braking action itself. Is this is the case, there's a problem in the brake wiring, etc.

Post back with the findings of this test and will procedure further.

Does the car have ABS brakes?

 

I just returned from the trip from Hell driving a possessed Camry! So after about 30 minutes on the freeway, cruise engaged, air conditioning on and working perfectly and listening to the CD I turned on the turn signal and the speedo bounced with each click of the tun signal. Then on turning the signal to the right, the speedo jumped and the transmission dropped to passing gear until I turned the signal off! The problems worsened as the trip progressed. The speedo started shimmering about 5-10 miles slower than my speed (had my GPS on). Then the speedo started jumping from 0 to 20 or so and shimmered some again then would pop back to the correct speed. I shut off all the accessories and the speedo seemed to work more consistently. When I arrived in my town I turned the air back on and the transmission immediately dropped out of gear and the engine revved. Turning the air off the car immediately had power again. I'm thinking vehicle speed sensor and what about the alternator? Not driving this car on the freeway until we figure this out. And thanks Joey, its comforting to have you on this one. Steve

 

Can only speculate but thinking as you, it may be an electrical issue.

Normally if the speedo IS working correctly so is the speed sensor system. Yours is not working correctly thus normally would point to speed sensor and wiring plus there is also a part for the speed sensor in the dash.

However.

There's your experiences occurring when AC is on, blinkers and brake lights, etc. These are all separate circuits but they do incur power usage when on. Assuming not all coincidences with speedo when each is used, then each system above is acting in some way in causing the problem. Each system draws power.

According to the wiring diagram the turn, AC and brake light system go to their appropriate fuses for their circuits. Then all receive power from a wire that runs to the alt. Then to the 100A alt fusible link, then to battery (this wire has a built-in fusible link). Except for wire to battery, all are white wires.

It could be a problem in this wiring or connections.

The speedo circuit is powered the Gauge fuse. This fuse also powers a tail/brake light out sensor in the trunk. If the issue were only linked to brake and possible turn signals would be looking at this sensor as it can fail. Or trunk wiring between trunk lid and chassis can fail due to flexing of harness. The result being shorts or crossed wires and electrical issues.

A problem with the wiring here or with the light sensor can cause power feedback into the Gauge fuse or perhaps a drain.

Suggest looking at the above wiring, plus:

Battery cables including connections at cable and condition of the large cable going to the 100A fusible link.

Battery cable ground connection.
Bonding wire between engine and chassis.
Connections at alt including grounding of alt.
Condition of fuses, fuse connection, etc.

 

You mention things I do not know about that I will research as to the wiring. I'm convinced the problem is electrical as again drove the car for about 30 minutes and was fine then began the speedo jumping. When I shut off AC, radio and all electrical devices no jumping. Blinkers and stop lights caused the speedo to jump. When I turned the air conditioning back on, again the speedo dropped to zero then quiver between 20-25 mph while actually at about 40 mph - the tach is not affected, and the engine would drop in and out of a lower gear. Had the alternator checked at AutoZone and it was fine, but the battery was reported as bad. I just can't get my head around no problems for 30 minutes. Wouldn't a short cause problems immediately?

 

Unfortunately electrical problems can be difficult to troubleshoot and can cause usual issues.

Suppose it is not a dead short? Water or corrosion can cause electrical cross over, but not enough to blow a fuse. Wiring damage in the trunk has caused back feeding into the dash console causing strange issues. A fusible link corroded to a point causing strange electrical problems to occur.

A low output alternator or battery issues can cause strange problems.

Was the battery load tested. Does the battery die if car is left overnight. Batteries can have internal shorts. If battery is bad, suggest starting here.

The electrical items you experience appear to be causing a electrical drain sufficient to draw the voltage or current down to a point other electrical systems no longer work normally.

If you don't have a wiring diagram suggest getting one. A Haynes manual is low price or try the library.

I suggest you do the items in the post dated 6/8 as could be bad wiring, connections, etc. You might try to measure voltage at the speed sensor B+ wire (may be Red/Blue color) to determine if it is dropping when you turn on the various items.

 

I began looking at the electrical wiring in the trunk and at the alternator. All I see are sheathed wires with harnessed connections - nothing looks bad to me. Looking under the hood and at the alternator was a joke! I just don't know enough for this. Too bad, as we love this car and it works perfectly, well except for its evil possession! I've got a good battery on my 2001 Camry that I am trading out and I'll try a speed sensor from the junk yard, but I'm afraid I'm tapped out. Thanks Joey for your patience and help. Wish this story had a good ending.