Dead Speedometer After Battery Jumped

GTtopLESS · Nov 2, 2009

What the hell is going on...I jumped my car(not sure why it was dead yet)...ever since then she is not good. Speedometer will not budge. She has died on me 3xs since this happened, but only when the ac was on. BTW, how bad is it to spike the clutch to restart her while rolling say...30mph? I did that 2xs....what yall think...

wmburns · Nov 2, 2009

check battery.

OBTW, today’s cars will not run with a totally dead battery. The battery must have some power to excite the field coil in the alternator. Without some functioning battery, the car will still die. Most likely when the alternator load suddenly increases.

First test the battery. Ensure the battery top and terminals are clean. Most likely the original problem is with the battery.

What else does/does not work? Lights, gauges, indicators?

Would be handy to know the car speed as reported by the PCM. If the PCM speed is zero, then you have damaged the VSS sensor in the transmission tail shaft. If the PCM speed is OK, then the problem is in the cluster

Also check fuses F2.21(5a), F2.5(15a), F2.34(20a), and F2.37(5a) in the central junction box (CJB). These fuses supply power to the cluster.

Recommend that each fuse be visually inspected. If no problem found, next remove each fuse one at a time, and test with an Ohm meter. Sometimes the fuse can be blown but not visible.

Check the fusible link to the alternator. Check the voltage between the main alternator B+ output and a good ground. If 12 volts, it is OK. Test the battery voltage while the engine is running. Should be around 14 volts. If not, may be bad alternator.

IMO, bump starting a car at 30MPH is OK as long as it it done in a reasonable gear. Don’t want to over rev the engine. 1st is too low at 30MPH. 2nd may be as well.

GTtopLESS · Nov 3, 2009

Thanks for the info. I am assuming the way to get a PCM readout I need to do the pre start-up sequence to get the digital readings via odometer? I will be taking her to get battery and alternator checked this afternoon. Everything now works that I jumped her the first time. I am hoping just a dead cell in battery and an easy fix.

wmburns · Nov 3, 2009

Need an ODB2 scanner to monitor operational data. The inexpensive ODB2 devices are code readers. Which means that can only read DTC codes (check engine). The advanced ODB2 scanners can monitor operational data.

For example:
AutoXray®

Scanner example: AutoXray®

Reader example: AutoXray®

There is a difference in price. The scanner can supply information that is difficult to get from any other source. For the home hobbyist, the $$'s can be tough to justify. Also, the local autoparts store will read DTC's for free. In that regard, buying just a reader for home use is marginal.

In my case, having a scanner has paid for itself multiple times over. On the other hand, I do a lot of work on my family's cars.

Note, Testing the VSS can be done the old fashion way. However, this requires detailed knowledge of the VSS output. Information that can be difficult to get (Ford factory service manuals). The home mechanic is limited to basic testing with a VOM meter (go/no go). For frequency type output, an O-scope is not reasonable (cheaper to buy the ODB2 scanner).

My vote is a new battery will fix you right up.

twogts4us · Nov 3, 2009

More great posts from wmburns -

You're officially now my favorite tech poster! Besides the thorough answers you provide, you also use proper grammar, punctuation, correct spelling and separate logically with paragraphs. These attributes makes the posts so much easier (and enjoyable) to read and digest.

Topless, I'd take your ride over to a local auto parts 'superstore' such as Advanced Auto, NAPA, or Auto Zone if you have any of these (or similar) in your area. They will, as wmburns stated, test your battery and alternator for free.

GTtopLESS · Nov 3, 2009

As you suggested, I got my alt. and battery tested, all good. I also got a SES light from this whole experience...the code pulled was P0720- Output Speed Sensor. Have any knowledge of this?...explains the speedo. Could the bump starts have caused that? ALSO I have a SpeedCal....could this cause these symptoms?

wmburns · Nov 3, 2009

Having problems with speedo and have a speed cal installed. Could be.

DTC P0720 is no VSS signal to PCM. Speed cal takes in the input from the original VSS and recreates it to send to the PCM. The unknown is if the speed cal is bad or the VSS is bad.

Suggest that you start with a visual inspection.

If I understand the post, no problem with battery. No problems with alt. Car dies suddenly like a bad battery. IMO, then it will get much more difficult after this.

What exactly was going on when the car quit? If coasting, most likely an IAC problem. Many people believe that cleaning the IAC is not an effective long term fix. Recommend to replace the IAC.

GTtopLESS · Nov 4, 2009

ok so last night I disconnected my neg terminal to clear computer. It worked. This am my speedo was working again and my idle was back to where it was before all this bs started. WTF? Why would I get a error code then turn out to still function?

wmburns · Nov 4, 2009

Welcome to the unknown

Welcome to cars/computers. If you want an answer, be prepared to dig deep.

There are two ways to look at this. One is to consider your self lucky and call it a day (glass half full).

The other (glass half empty) is that problems do not fix themselves and this issue will come back.

OBTW; it is an important detail about the speed cal install. Especially with a speedometer problem. The details can help prevent chasing after wild geese.

OBTW2; if you were coasting (engine disengaged) at the time it died, this is most likely an IAC problem. It never hurts to do a through look over for vacuum leaks.

OBTW3; I am not sure that I understand how a battery could need a jump and then be OK. Today's cars will not run correctly without a solid battery. The PCM and other electronics will flake out without a stable power source (voltage). The battery is also vital to the function of the alternator. Gone are the days of jump starting a car with a dead battery.

patman0911 · Nov 4, 2009

Weird, maybe you lucked out There's a tiny possibility that one of those times the computer was on the edge of not getting enough voltage to run, the volatile memory got filled with garbage data and the car wasn't running well enough for the bad values to eventually correct themselves... maybe.

Doesn't the computer use the VSS to determine when the car is not moving and it's cool to go to low idle? Perhaps since the computer thought the car was stationary all the time, it was dropping RPMs too fast and overshooting the idle RPMs and dying. That still seems unlikely - that never happens while revving in the driveway - always hangs for a few seconds somewhere in the 800~1200 RPM range before dropping down to 650. PI cars do seem to be more sensitive to idle issues and stalling though.

I still like my first unlikely theory better but it doesn't really explain the speedo problems unless the SpeedCal crashed and hung up from low-voltage. Is the SpeedCal always powered or is it switched with the ignition? That should've cleared up by just turning the car off and on unless it's always on.

GTtopLESS · Nov 4, 2009

Well I tend to be a half empty kind of guy....When I had my battery tested it had lost a few cranking amps, but evidently it is ok to operate the car. Car still running great today. I dont know much about the Speed Cal; it was already on her when I purchased. Being how annoyed I get about unfinished posts I will bring this back if issues reccur. Thanks for all the help!

kstng50 · Nov 9, 2009

I had the same problem with the speedometer after jumping the battery. My car also did the stalling when the speedo was not working. I did the same disconected the battery and hooked it back up and all was good again. I know my speedcal is always powered on it is powered from the cigarette lighter. I'm wondering if this is what keeps killing my battery since I dont drive the car that often.

wmburns · Nov 9, 2009

kstng50 said:
I had the same problem with the speedometer after jumping the battery. My car also did the stalling when the speedo was not working. I did the same disconected the battery and hooked it back up and all was good again. I know my speedcal is always powered on it is powered from the cigarette lighter. I'm wondering if this is what keeps killing my battery since I dont drive the car that often.

I would say yes because the cigarette lighter is hot at all times (no key needed). This sets up a situation with a slow drain on the battery.

I am no expert on speed cal, but I would thing it should be on a "key on" circuit. From other posts I have read, the speed cal can be powered by the same circuit as the heated O2 sensors. Then it is only powered when the key is on.

GDawg · Nov 9, 2009

twogts4us said:
More great posts from wmburns -

I am in his fan club with you brother. Since 'burns joined in August he has truely given some good advice. I know that I'm learning from him.

GTtopLESS · Nov 9, 2009

My SpeeCal is also powered by cig. lighter...Well, looks like this could be a case solved issue. I had THE EXACT symptoms with same cure. Either find a "key on" power source or crank your ride every 2 days. BTW, KSTNG how many days would you say it takes to kill your battery? Mine in less than 55hrs!

kstng50 · Nov 10, 2009

Im not that sure how fast it dies when I do drive the car it is on the weekend and sometime not even every weekend anymore. It seemes to die faster then usual now because I dont think it ever gets a chance to fully recharge the battery. Last time I jumped it and took it for a good drive it stayed charged for over a week. I was going to pull the fuse on the cig lighter and see if it still drains but now it is starting to get that time to put her away for the winter so I will prob just take the battery out and fix it in the spring.

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