I've seen it mentioned more than a few times here about 'hard resets"
by disconnecting the Negative from the battery post and then touching it to the positive post of the battery. The theory is that this hard reset allows all of the electric energy stored in the capacitors on the multitude of processor boards to drain and creates a more robust and complete "reboot" of the vehicles' processors and electronics when the battery cable is connected to the negative terminal again.

I'm hesitant to do this, should I be?
Has anyone ever used the "hard reset" before?
Does it work better than just disconnecting the cable for a half hour or so?
Once the "hard rest" is used does it create any other trouble? or recalibrations required?

Thanks.

 

What problem are you trying to fix?

 

I just did a few mods to my 07 and disconnected the negative battery terminal for a couple hours while I was working on it. Never heard of touching terminals before and to be honest too afraid to try this in case I fry an ECU or something!

 

It's identical to a longish disconnect. Mainly clears learned values (in KAM) such as fuel trims. You'll have to reset a few minor things like one-touch windows and radio presets. Car may idle a bit roughly till it relearns. You'll have P1000 till it becomes P1111 or else fails to if you've something blocking an OBD monitor.

Don't do it without a reason.

 

I'm trying to reset a persistent P1647 upstream O2 sensor code. Tried replacing, swapping right and left and the blasted code and CEL remains!
Also P1254 TPS sensor/gas pedal code, sometimes resulting in Restricted Performance and Occasional Limp Mode. Dealer says they can't reprogram the PCU and it needs to be replaced, only $2K!

 

Have you looked at / carried out JTB00188 for P1254?

I'd start there I think.

OK, if I had 2 codes as you do I probably would NOT start there LOL. I'd start with the Electrical Guide and hunt hard for any wiring that might cause both faults. But I like a puzzle and don't like to pay for a reflash that's maybe a bit speculative.

(I'd also test the O2 sensors, not trusting any shop, but I have tools that would let me and quite likely you don't.)

I can't see any kind of disconnect fixing the codes. But forcing a relearn might (that's might) help in the somewhat unlikely situation that the car is kinda stuck with old not so good values. Honestly that's grasping at straws. I really would go with the Electrical Guide and brain power.

 

The jag tech said he checked the wires and harnesses and there was no short when he checked the resistance. The car runs fine most of the time which makes me think its not a complete brain fart in the PCM? I have a new Denso O2 sensor and I'm planning to remove the Throttle body and send it to a shop in Tennessee for rebuild and see how it goes. I thought maybe this "hard reset" could possibly reboot all the controllers but it may be too optimistic and perhaps fatal?

 

The Jag dealer can't access the PCM with the JTB00188 upgrade, says the PCM won't accept the new software.

 

It won't hurt anything, but I wouldn't expect it to fix anything either. You are saying you already put a brand new OEM O2 sensor in? If so, then the ECU could be damaged, as it is responsible for sending the signal to heat the O2 sensor (that code is for the heating element of the sensor) or the sensor could be faulty/defective if there is no damage to the wiring at all.

 

Finding another person to work on the car looks attractive. Jag indy, preferably.

Reflashing ought either to work (as usual) or be debuggable (bad wire or whatever). Fixing an O2 or diagnosing it - e.g. through OBD - isn't rocket science to someone in the trade, or at least shouldn't be. These are very common sensors nowadays.

 

I'm planning to replace my cranky P1647 O2 sensor with a brand new one and then remove the throttle body this weekend and send to ASI in Tennessee on Monday in an attempt to fix the P1254 code. I spoke to a service tech at ASI he said they repair these TB all the time, clean and recalibrate the TPS and return with a lifetime warranty all for $289. He was very optimistic that any Restricted Performance/Limp mode trouble caused by gas pedal-TPS codes or trouble would be solved by their repair. Has any one ever used this service or this repair on an STR throttle body? If so, was it successful?

 

Gas pedal (APP) has its own codes, distinct from TB, distinct from TPS.

 

What O2 sensor did you install? Brand and Model number.

Take a look at my thread on fixing this same O2 heater code on my 2005 STR.

https://www.jaguarforums.com/forum/s...6-p1647-86397/

There are others and a search is very useful!
.
.
.

 

Denso #234-9030 for the upstream driver's side P1647 code.

 

Replaced the driver's side upstream O2 sensor with a brand new Denso. Used the scanner and cleared the P1647 code. Everything was OK for about 10 minutes and then the P1647 code comes back again!
Somehow the P1254 Throttle Body code was cleared and has not reappeared yet. I've found that if the car is started and turned off before it is allowed to warm up to operating temperature, the P1254 code and RESTRICTED PERFORMANCE can appear sometimes.

 

Sounds like you have an ECU issue.

 

That's what I'm thinking..., any ideas?

 

Bad battery #1. Bad fuse(/relay, if any)/wiring/connector #2. A mite awkward to meter it through.

 

Battery is about a year old and strong, checked O2 heater fuse, looks OK.
Cleaned, tightened and lubed the battery connections and the wimpy negative ground to the body in the trunk. I can't believe all the power to the car goes thru that tiny 8mm negative ring terminal? I cleaned that up too.