1997 C5 Coupe

I get constant Low Tire Pressure messages for all 4 tires which are inflated to spec. When I reset the warning messages and check the readings, the DIC displays correct pressures. From this, I conclude that the TPMs are sending the correct data to the RFA. (I have also replaced the TPMs with new ones with the same results.)

If I'm correct in my understanding that the BCM receives the raw data from the RFA, then generates messages based on that data, it would seem that the BCM is responsible for the bad messages and warnings. Is there something I can try without replacing the BCM? Would relearning the TPMs be worth trying?

I've been living with this annoying situation for a couple of years, and I really am tired of it. Can anyone help?

Many thanks,
Jerry

 

The relearning procedure should have been performed when you replaced the TPMS sensor/transmitter. If it was not done then, it needs to be done before any more troubleshooting takes place. Doing the learning procedure is cheaper than any thing else, and it is what I would try before doing anything that would cost me money. After it's done and you still have the exact problems then I would guess that the problem is else where and the BCM may be the problem.

 

I have no doubt the relearning procedure was performed when the TPMs were replaced. Else, how could I get any data at all from them? What I'm asking is if the process of relearning *again* has any value in perhaps butt-kicking the BCM into some sort of re-initialization? (Think software bug in Windoze on your PC, and you solve it by power cycling your PC. Imperfect analogy, I know.)

I will do the relearn procedure again as soon as I locate a strong magnet. In the meantime, can anyone think of anything else to try before spending a few hundred on a new BCM?

Thanks,
Jerry

 

Yes, I know it's been 2.5 years since my original post. I do tend to procrastinate.

No other problems with my electrical system, battery is new and fully charged, key fobs work great, AC is good, etc... Just this constant Low Tire Pressure warning.

So today, I "re-learned" the TPM sensors using a magnet according to instructions posted on this forum. All successful. Drove to the service station and set the tire pressure to 32 psi (according to an accurate guage). Driving off, I got Low Tire Pressure warning for all four tires, after which the DIC read 29-30psi for all four.

So the TPMs are sending data. The RFA is receiving the data. The data is correct (within accuracy limits). The *warning* is bogus. This is NOT an intermittent problem, and has been present consistently for over four years through at least two battery replacement cycles.

That seems to eliminate faulty TPMs, bad RFA, ground issues, and connector issues. Am I correct in concluding that the only thing left is a bad BCM? Anything else I can check?

Oh, here are the DTC codes I grabbed tonight:

40 BCM:
B2592 H (Column Lock/Unlock Drive B)

A0 LDCM:
B2282 H (Battery #1 Circuit)
B2284 H (Battery #2 Circuit)
B2262 H (Horizontal Position Sensor Circuit)
B2264 H (Vertical Position Sensor Circuit)
U1064 H (Lost Communications with BCM)

A1 RDCM:
B2283 H (Battery #1 Circuit)
B2285 H (Battery #2 Circuit)
B2263 H (Horizontal Position Sensor Circuit)
B2265 H (Vertical Position Sensor Circuit)
U1064 H (Lost Communications with BCM)

B0 RFA:
C2110 H (Right Rear TPM Sensor Malfunction)

Again, all TPMs are working consistently. The Column Lock was bypassed 15 years ago when it malfunctioned. Any ideas?

Thanks much!

 

I don't think you can discount the RFA, but I agree you can discount the TPMS sensors. I have no technical basis to say it is the RFA versus the BCM. Also, it would be easy to swap one with another C5 to test. That is what I would do if I didn't have a spare BCM to try. Remember if you put in another BCM to try you will need to at least have it programmed to match your key resistance (unless you got lucky). There is a way to get around that on a temp basis if you need to do that let us know.

PS: All your codes show H. Have you just not bothered to clear them of did you pull them after you shut off the car.

 

What stands out to me is the C2110H (RR TPMS) code. Also I find it odd that you get a low tire pressure warning when the pressures read 29-30 psi. You should not get a low tire pressure light unless it drops to at least 25 psi.

The tire pressure sensors send a frequency to the RFA which translates the frequency to a psi value. Through serial data the RFA sends the tire pressure values to the IPC. The IPC then displays the tire pressures. The receiver is what sends the IPC a message to display any tire pressure warning messages.

If an external tire pressure gauge reads close to what the IPC displays as pressure, I would eliminate the tire pressure sensors and IPC as a cause of failure.

I'm leaning towards the RFA receiver sending a false failure signal to the IPC. Try jacking up the pressures to say 43 psi or so, or even at 24psi, and run it around the block. See if you get a correct error message (either too high or low tire pressure).

 

Thanks for all the prompt and detailed replies! This forum is the greatest.

Yeah, that code probably was thrown a few weeks ago when I saw a "Service TPM System" message. It was a cold day and the RR sensor takes longer than all the other TPMs to report pressure (2-3 miles). I think this time it was just over the threshold for throwing the code. No repeat since. So I guess that RR TPM is probably marginal and ought to be replaced eventually.

Did this today and I do get a "High Tire Pressure" message for that tire. Unless the pressure is too high, I always get "Low Tire Pressure" warnings.

Cleared all codes, went for a 30 minute drive around town and checked codes without shutting off the engine. No codes.

Yep, that sounds right. Had a battery go bad a few months ago and didn't think to clear the codes then.

Three of my sensors report tire pressure within half a block or so. The RR usually takes a couple of miles. Sorry for my imprecise wording.

Carpet has never shown evidence of any leaks.

From my reading on this forum, I understood that the RFA received the data from the TPMs, and sent it raw to the BCM which then evaluated the data to issue warnings to the IPC. Is that not correct?

If it's the RFA that generates the warning message, then yes I agree that it's more likely to be the RFA than the BCM.

Otherwise, if the BCM generates the warning messages, the fault could only be in the RFA if the data were being corrupted before being sent to the BCM. And I guess the last possibility could be that the connector from the RFA to the BCM has a bad connection.

Can someone confirm which module generates the warning message?

 

According to the FSM in the Service Information for Tire Pressure Monitoring System:

"Receiver" in this case is the receiver for the RFA. No mention of the BCM. The manual also discusses the barometric reading taken from the PCM at vehicle startup being sent to the RFA to compensate the tire pressure readings. This implies that the pressure calculations and proper message determination is done in the RFA.

Discussion in the FSM on the BCM does not mention the TPMS at all.

 

The RFA sends tire pressure data and fault signals directly to the IPC through serial data.

Wrong, RFA does send tire pressure related fault codes directly to the IPC.

From the FSM:
"The receiver also warns the driver of a tire over or under inflation condition. If the TPM sensors transmit a reading of over 289 kPa (42 psi), the receiver will send a message to the IPC to display the HIGH TIRE PRESSURE warning message. If a tire pressure reading between 34–172 kPa (5–25 psi) is sent, the receiver sends a message to the IPC to display the LOW TIRE PRESSURE warning message. If the reading sent is under 34 kPa (5 psi), a FLAT TIRE message will appear."

Something worth trying... disconnect the RFA and see what happens.

 

Don't take the FSM so literally. The information goes to the IPC via the BCM. The BCM is the "Traffic Cop" for this type of information going to the IPC.

 

Circuit # 1045 (pink) is the serial data line that directly connects the RCDLR to the IPC.

 

There's a lot of great info here, but let me ask a very basic question...How old are the TPMSs? Don't their batteries have a useful life of about 10 years?

 

Mine are about 3 years old now. But this problem predates changing them out.

 

I'm curious what year this schematic is from. My 2001 FSM is different. It only shows a feed directly into the serial bus not via any other component. BTW, your schematic is not to the IPC, but to the fuse box in the passenger compartment. Apparently in your schematic the data is just passed thru the fuse box to the serial bus. The HVAC fuse 27 there powers the RFA module.

I think where the message is created is still up to speculation.

 

The schematic I used is from a 2000 Corvette. Here is the schematic for a 1997 which the OP has:


You are right, the serial data does not show a direct path to the IPC, I saw "instrument panel" and automatically assumed IPC. I apologize.

But according to service info, the RFA is what sends tire pressure error messages. And if there is an erroneous error message being displayed on the IPC, I think the safe bet is the RFA receiver itself since the tire pressures read accurate.

 

n8dogg, at this point I think the best thing for him to do is to try a new/different RFA module. Even if it does not send the error message it could still be sending bad data. It is also cheaper and easier to replace than the BCM. He might even be able to borrow one from a friend to try. If I wanted to resolve this issue, that is what I would do. What say you? And thanks for your input on this. Mr. Sam

PS: I am curious why they ran the serial bus feed thru the fuse box. May have just been easier from a wire bundling aspect. Obviously they changed that in 2001. I am glad you posted that so I know it is routed differently for earlier cars.

 

Thanks for all the great input, guys! As soon as I get some time, my next step is to check the RFA connectors and wires, then swap it if necessary. Now if I can just figure out how to remove the trim panel without breaking it... Anyone have an R&R diagram?

 

Agreed, RFA swap would be a good next step.

Not sure why the RFA serial data line goes through the fuse box. You can see in my attachment, this is the only serial data circuit that does this. It does seem weird because the star connectors are right next to the fuse panel. Probably was just easier to make the harness that way.

 

I have the FSM at home and will let you know what it says about the R&R of the panel if no one else beats me to it.

PS: Make sure you get the earlier RFA for your car, I believe in 2000 or 2001 the design changed along with newer/different TPMS sensors.

 

Here is the info on removal. Installation is just the opposite. The arrow points to the front of the car. It looks like the "insulator" has a plastic retainer pin at the rear. Let us know what you learn about removal.