My 95 XJS 4.0 transmission light came on after a sudden stop. Limped it home. Next morning the light was of. Stayed off fo a couple of weeks, then came back on after a quick stop along with the check engine light. Next morning transmission light was off but check engine light was still on. Had a parts store check it with an OBD meter showed a code P0727. I read on this forum that an XJR with same code turned out to be Cam position sensor. A mechanic friend said that on my car check the Trottle position sensor. I don’t want to start throwing parts at it. Any help will be greatly appreciated.

 

G Man,

I'm not sure why your mechanic would tell you start with the the TPS. A P0727 is a standard OBDII code. It is thrown if the engine speed input signal is lost. So, a sudden stall or engine rev drop below 95rpm could cause it. The Transmission light is usually just a consequence not typically a transmission fault.

You mentioned that both times it was after a "quick stop". What does that mean? Did you brake o a halt suddenly but the engine was still running or do you mean that the engine stalled?

If the engine stalled or revs dropped very low, start looking for a cause such as a sticking EGR valve, even a failing coil. If the engine is cutting out, that COULD be indicative of a crank sensor failing.

Start by reading and clearing any engine codes.

Good luck

Paul

 

The engine didn’t cut out or stall. I just had to brake hard. That’s when the transmission light came on. The 2nd time it came uon was also a hard stop. That time the check engine light also came on and stayed on the transmission light did come back on when restated 5he next day.

 

P0727 is not a helpful code, so I can understand why your mechanic would take a stab at it...unfortunately, if you're going to start guessing and throwing parts at it, a $200+ TPS is not where I would start.

As mentioned above the following can cause these problems:
1. crank position sensor (CKPS) - fairly common, fairly inexpensive, fairly easy to replace on your own.
2. EGR - fairly common, more expensive, fairly easy to replace on your own - I'd wait for a code P400 before I replaced this. Some people have had success with cleaning it, but I haven't.
3. idle air control valve (IACV) - fairly common, fairly inexpensive, fairly easy to replace on your own (be careful with the 5.5mm bolts holding it in place, they will snap because of the loctite used.)

After that, we get to:
a. oxygen sensors, which need to be replaced every 50k miles or so anyways. You're from the US, so I believe you have four of them. You should be able to replace these yourself.
b. coils - easy to replace, but they are fairly pricey, and no good way to bench test them. Cheap ones will not last, don't tempt yourself.
c. spark plugs - very cheap, easy to replace, definitely do these if you're replacing coils
d. TPS - easy to replace, costly to buy.
e. MAF sensor, easy to replace, not a common fault.

At the end of the day, there really isn't a whole lot that you would want to pay a mechanic to do. One thing I haven't put on the list is to check for vacuum leaks and oil in the spark plug wells. Both can trigger a P0727 code. I would definitely check for these first. It could simply be a coil or two getting drowned in oil, which is a common failure.

 

Thank both of you for your responses. Now I feel I have a place to start.

 

G Man,

As mentioned, the code gets thrown when there's a drop in the engine speed signal. So even deterioration of the wiring from the ecu to the TCM can exacerbate the Transmission warning Light illuminating.

I know it's difficult, but next time you brake hard, try and quickly see if the rev counter drops right down as this is probably the interim problem causing the code to be thrown.

Paul

 

Your mechanic is right. The TPS is dirty so its not giving back proper telemetry. Read this.

https://www.jaguarforums.com/forum/x...-light-261367/

https://www.jaguarforums.com/forum/x...cation-214280/
dont even have to throw parts at it. Im very familiar with this issue. Hoping people remember my comments because way too many folks here seem to always forget it

 

Brewtech, the TPS for the 95 and 96 six cylinder engines are not the same TPS that you refer to in your posts.

The AJ16 engines use a different TPS. It is a completely sealed TPS with nothing to drill and nothing to drain.

 

Im still convinced that when the TPS go iffy, it will trigger limp mode. Whether its AJ6 or AJ16. I always preferred the AJ16 over the AJ6 but Ford really did make the AJ16 a little harder to diagnose and also added a few changes that complicate things a bit more. The TPS can at least be tested on the car. A CPS is kinda good measure to simply replace since it can go faulty too

 

the TPS is not reliably tested. It’s a part that has a history of bench testing well, but causes problems anyways.

 

Thats great info Vee!