2005 Sebring Convertible GTC 6 cyl 2.7l 167 CID. 194,000 miles. Goes into transmission "limp" mode intermittently. First happened about 2 months ago- once per 40 starts. Now happening about 1 in 3 starts. Goes into "limp" mode immediately after starting car, but can also start in completely normal operation. Re-starting the car will (eventually) clear the problem. The problem has now progressed to where it sometimes causes all the "PRNDL3" gear selectors to have boxes around them and ALWAYS AT THE SAME TIME it disables both the speedometer and the odometer needles from updating- but tachometer still works/ tranny is in "limp home" mode. When this happens, I restart the car, and all problems (usually including "limp mode") disappear. The car runs fine otherwise- no missing, no lack of acceleration, no other problems. NEVER a "Check Engine light"!! My OBD looses connection- took it to 2 auto parts stores- one couldn't get their OBD to work with my car; 2nd place got codes: P0700 (Transmission Control Sys (MIL Request) (I know from forum that this is a "general" warning); P1603 (PCM Internal Dual-Port RAM Comm Failure); and U0101 (Lost Comm with TCM). Where do you recommend I start the troubleshooting? (I was thinking of replacing the Speed Sensor when I saw an "old" P0501 code, but now I'm doubtful. Oil-changing business told me one battery cell was low and they thought that could be a problem (but I've never had a starting problem). Looking for suggestions where to start without throwing in random parts. Your help is much appreciated!!

 

Batteries and connections on the modern cars (yes 05 is modern enough) are critical to all computer controlled functions.
Each start/restart turns computers on /off at set rates, that is why the issue comes and goes.
If your battery is 5+ years old I would replace it regardless of the "it starts ok"
A shop already told you one cell was weak so it needs to go anyway.
Also disassemble and clean all connections from the battery to the jump post and grounds, they always "look good" but need to be serviced.

No Parts Cannon!

 

OK I changed he battery & cleaned all connections until shiny. The "PRNDL3" all indicator light-up + no speedometer + no odometer + "limp home" mode happened once more (In about 20 starts). The "limp mode only" hasn't happened in the past 2 days. Puzzling. Things are changing but not sure they're improving, BTW the old battery measured 12.5 V (no connection), the new battery measures 12.75 V (no connection), and the voltage measured at the battery terminals when the engine is running is 14.0 V DC. Any suggestions?

 

I wouldn't rule out a continuing electrical problem. You replaced the battery, but have you watched the voltage in real time with the engine running? after at least 30 seconds (usually much sooner though) the voltage should stay stable... +/- 0.2v. If it's swinging all over the place (+/- 0.5v or greater) you likely have an alternator problem. Worst case you have a failing ECU.

 

OK I checked the voltage during operation- I saw maximum voltage swings from 13.95 - 14.10 V DC, but mostly 14.04 +/- 0.05 V (observed ~ 2 minutes each time). This is over the course of 10 engine starts, waiting from 30 seconds to 15 minutes between starts. Battery measured 12.85 V immediately after engine stop, decreased to 12.67 V 15 minutes later. Did not replicate problem during these 10 starts. I watched during cranking- the digital multimeter dipped to 10.5 Volts on one sample (maybe 0.25 seconds), but immediately went to 14.04 V after engine started. While I have heard that faulty alternators can cause sensor problems, it should be noted that this problem occurs immediately after engine start, NOT while driving down the road. I suspect some sensor is misfiring during the engine start process, and latching the status. I can shift between gears even though the PRNDL3 indicators are all on. Thinking about checking wiring to TCM, etc. Haven't checked ECM- on this car, does ECM = PCM + TCM?? So I should check PCM & TCM? Or another module entirely? Thanks in advance for your help!!

 

Ok, I think we can rule out, for the time being, issues with the battery and/or charging. Those voltage numbers look perfect in my book.

The two codes P1603 and U0101 are worrisome. They could indicate the ECU is failing.
Note there's no separate PCM/TCM on the 05/06 model years (and some late 04s apparently as well).

Note a bad unit isn't a death sentence for the car; there's many services out there that will provide you with a repair/replacement of yours.

If i'm reading your post correctly, the problem hasn't re-occurred frequently? Have you cleared the codes as well?

 

As of the last 2 days, the problem is occurring MUCH less frequently. "Limp mode" (by itself) was happening maybe 1 out of 4 starts over the past month (was getting worse/ more often over a month). Now the PRNDL3 lit + no speedo + no odomtr + Limp mode is happening a few times (never saw this before!) a week. I had the following codes (stored from probably the past 5 years) on Friday (2 days ago): P0300/ P0700/ P0501; 2ndary codes:U0101/ P1603 / P0562/ P0891 / P0714 / P0218 / P0713 / P0562 / P0122 / P0883 / P0123 /P0124. After I cleared these codes, the car worked MUCH better (almost seemed like clearing the code fixed the problem (I don't believe that, though)). Started it 17 times (a minute+ between every start) before the PRNDL3 issue happened again. That's when I have "only" the P1603, P0700 & U0101 Codes. Today I changed the battery, cleared the codes, drove around for an hour, and got one PRNDL3 issue after the 14th (?) start. My OBD2 reader has problems "staying connected" to my car, so I don't have new codes yet. Odd how this pattern is changing- not truly random.

 

So, long story shorter: I have experienced ZERO simple "limp home only" modes since clearing the codes, but I still get the PRNDL3 box lit up + no speedo + no odo + limp mode once in a while. Changing battery didn't seem to change things.

 

From the sounds of it, I think it did.
If only the cluster is now malfunctioning, but the transmission is shifting properly. then it would seem you had multiple problems: an unhappy ECU (due to battery/voltage), and potentially a malfunctioning cluster.
it's late so I don't have time to deep dive into the manual to bolster my suspicions. Maybe tomorrow.

 

3.11 MECHANICAL INSTRUMENT
CLUSTER
The Mechanical Instrument Cluster (MIC) is divided into 4 sections. Primary gauges (Speedometer
and Tachometer), secondary gauges (Fuel Level,
Engine Coolant Temperature), PCI bus enabled
indicator lamps and hardwired enabled indicator
lamps.
The gauge mechanisms function in the same way.
The main differences are in the face and size of the
gauge.

The Oil Pressure, Brake Warning, Turn Signal
and Fog Lamp indicators are directly wired to the
circuits that they are indicators for. These indicators are located in, but not controlled by, the MIC
and are not part of any MIC self test or diagnostic.
All indicators are replaceable bulbs or LEDs.
The PCM sends a gauge position message to the
BCM through the PCI bus. The MIC receives this
message from the BCM, translates it, and positions
the gauges. The BCM also sends messages to the
MIC to actuate all PCI controlled indicators. These
messages are received when the Ignition Switch is
in the RUN or START position.
When the ignition Switch is turned to the RUN
position, a bulb-check is performed. This consists of
activating the PCI bus controlled indicators for
approximately 2 to 4 seconds. By holding the TRIP/
RESET button in while turning the Ignition Switch
to the RUN position, you can activate the MIC Self
Test.

The Following indicators are controlled by PCI
bus messages:
• Malfunction Indicator Lamp
• Charging System Warning Indicator
• Engine Coolant Temperature Indicator
• Cruise Engaged Indicator
• Airbag Warning Indicator
• Low Fuel Indicator
• ABS Warning Indicator
• High Beam Indicator
• Traction Control Indicator

The following indicators are hardwired and not
controlled by PCI bus messages:
• Seat Belt Indicator
• Oil Pressure Indicator
• Brake Warning Indicator
• VTSS Indicator
• Turn Signal Indicators
• Fog Lamp Indicators
• Traction Control Switch