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Wiring diagram reading for troubleshooting parking aid sensors
As a mechanical engineer, reading electrical diagrams can sometimes feel like you're watching a horror movie, complete with a sense of dread and jump scares. Can somebody who is comfortable with these diagrams please confirm if I am doing this correctly?
Objective: Locating parking aid fuse as part of troubleshooting the silent sensors.
- On Fig 19.1 of the wiring diagram, I see that the parking aid control module is powered by switched position 12 (12I). - At the bottom of the figure, I see that 12I is addressed on Figure 1.4. - On Fig 1.4, I see that 12I runs through 5A fuse #13 in the trunk fuse box => go check fuse #13.
Does this make sense or am I missing something? Thanks!
Yes, you are reading it correctly (although you've put the red box in the wrong place on the screengrab). The I after the 12 means position one on the ignition switch. II means position two.
Great, thanks!
Staying consistent with my luck lately, the fuse is just fine, so checking harness and connectors next. It also occurred to me that the sensors and chime have had to work pretty hard lately with my trying to get the backup camera going, meaning I've been standing with my head in the trunk and the shifter in reverse (ignition on, engine off of course!) for extended periods of time. Maybe the parking sensor module doesn't dissipate heat well and can't handle a a few minutes of constant action?
If I were you I'd check for power and ground at the module and check that "reverse lamps activated" line is coming on when in reverse - maybe you did something to it when fitting your backup camera.
I doubt you've burnt out the module, but I suppose it's possible.
FWIW, folks have reported before that the sensors, when active, emit a faint clicking sound from up close. That would be a scenario where the sounder is somehow no longer functional, but the rest of the system still is.
As the wiring diagram shows, there is apparently a way to run diagnostic on this box (serial line) but you would need the right scanner/software.
Also, there is an input based on the reverse light that you could, carefully, activate to test.
FWIW, folks have reported before that the sensors, when active, emit a faint clicking sound from up close. That would be a scenario where the sounder is somehow no longer functional, but the rest of the system still is.
As the wiring diagram shows, there is apparently a way to run diagnostic on this box (serial line) but you would need the right scanner/software.
Also, there is an input based on the reverse light that you could, carefully, activate to test.
Best of luck, keep us posted.
Yeah, I'm going to get as scanner shortly. I see several people use the iCarsoft LR II, so will probably be my pick.
The sensors do not click (none of them), so more likely the module or the wiring rather than the sounder.
Thanks!
The sensors do not click (none of them), so more likely the module or the wiring rather than the sounder.
Did you check the fuse is actually powered when needed? There is usually a small clearance area on the fuse for the tip of a meter probe. Capt obvious warning: if the module is not powered at all, you will not be able to get diagnostic from it and a scanner won't help.
Did you check the fuse is actually powered when needed? There is usually a small clearance area on the fuse for the tip of a meter probe. Capt obvious warning: if the module is not powered at all, you will not be able to get diagnostic from it and a scanner won't help.
Best of luck, keep us posted.
So after ordering and receiving electrical tools better suited for automotive than those I was using previously I could properly test the pins on the module and on the connectors. What I found is that the module has its ground (pin16), has its +12V when the ignition is in I or II (pin1), and outputs +12V to the the sensor connector when reverse is engaged (pin6). I was going to test at the harness connector next, but decided to give the sensors a close listen and, sure enough, they're clicking away, just a lot more quietly than I expected. Could have saved myself a lot of time if I had listened properly the first time, but much better to learn slowly than not at all
So the next thing to check is if the module receives the sensor input properly, which I think can only be done by piercing a needle conductor through the wire insulation with the connector in place. I can't find any info on what that signal should look like, but guessing it's a pulse voltage since the relays in the sensors go on and off constantly when triggered? Anybody know?
Thanks!
So the next thing to check is if the module receives the sensor input properly, which I think can only be done by piercing a needle conductor through the wire insulation with the connector in place. I can't find any info on what that signal should look like, but guessing it's a pulse voltage since the relays in the sensors go on and off constantly when triggered? Anybody know?
Thanks!
If all the sensors are clicking, then I doubt if somehow every single one of them doesn't have its return wire connected, or if indeed there is a separate return wire - looking at the wiring diagram it looks like each sensor has power and ground and a single trigger/echo wire, so if they are clicking, they are working.
Have you checked the speaker in the back of the car (behind the centre arm rest)? Is it connected, does it work? That's what I would check next.
If all the sensors are clicking, then I doubt if somehow every single one of them doesn't have its return wire connected, or if indeed there is a separate return wire - looking at the wiring diagram it looks like each sensor has power and ground and a single trigger/echo wire, so if they are clicking, they are working.
Have you checked the speaker in the back of the car (behind the centre arm rest)? Is it connected, does it work? That's what I would check next.
dibbit and fmertz,
Many thanks for staying with me on this!
Yes, the speaker is connected but when I check the voltage over the connector pins, I get 12V regardless of whether reverse is engaged or not (well, 12.2V in key position I and 11.8V in position II). Just like the diagram doesn't tell me what the return signal from the sensors should be, it's not clear (to me at least) what signal the module feeds to the speaker when triggered, but I doubt there is supposed to be a constant 12V over it? Is this telling me it's a module failure after all?
Speakers need to be fed a variable current to make a sound, so if both terminals are at a constant 12V, there will be no sound (double check this). When activated, the current should be the literal waveform of the sound Jaguar wanted (that beep-beep). Standard "La" is 440Hz, so the signal should be oscillating at a frequency of hundreds of times per second. Your meter might not be able to see that. Double check the resistance of the speaker. To my superficial knowledge, speakers come in 4 Ohm and 8 Ohm variety.
I'm not really sure what you can tell with your meter on DC voltage. At least on AC voltage you might expect to get some kind of value when the speakers are supposed to be beeping. This is where a cheap oscilloscope really comes in useful, so you can see what is going on. Or, another essential tool IMHO, is a crystal earpiece. Just touch one wire of the earpiece to the audiio output and you will hear if it is making noise, eg:-
It is indeed 12V over the speaker connector, regardless of if in reverse or not. There is no continuity over the speaker terminals (resistance reads infinite). Can it be that the speaker has a built-in relay that is activated by the constant 12V to put the speaker on "stand-by"? Seems cumbersome, but I know nothing about speaker design. If not, then it seems like there's a short in the module such that it's outputting 12V constantly, although I would have thought that would cause the module to fail altogether?
I ordered the crystal ear piece, will be delivered tomorrow. And today I should receive my OBD scanner, will be very interesting to see what it shows.
How cheap of an oscilloscope do you think will be sufficient, something like this?
It's funny, for the amount of money I'm prepared to spend on this troubleshooting, I could easily buy a new module and speaker, but the learning experience has a lot of value to me. Learning to work and troubleshoot the electronics seems essential to keep this marvelous machine running and I plan/hope to keep it around for the very long term.
On the face of it, your speaker is dead. You might want to check, there are normally _tiny_ wires linking the soldering terminals to the coil. Maybe one or both broke during your more extensive project earlier. You should be able to re-solder them, or just replace the speaker altogether. You should definitely have some (fairly low, a few Ohm) resistance between the speaker terminals.
I managed to open the speaker housing without breaking it and confirmed continuity between each terminal pin and its solder to the coil wire, but no continuity between the two solders joints, so the coil wire must be severed then. It looks like the membrane is glued in place over the wire so I doubt it's possible to solder it without rupturing the membrane in the process.
For reference, the speaker is DIGISOUND F/BMS3650 and this site has them listed for $1.35 + $7 shipping to the US.
Hopefully this is the end of this particular little saga, and I now know to disconnect the parking aid module before re-attempting the backup camera project.
Again, many thanks!
Wiring diagram reading for troubleshooting parking aid sensors
