[Scottrodds]

Ok. I changed the ipdm. Still won’t start. I rechecked all the terminals we talked about again but this time with a DVOM. All the terminals have voltage as normal except 80. Still nothing there. I checked on the brake switch. It is giving me the message to press brake, when I push the brake it doesn’t go off. I also cycled the push button like jbarnett250 said and it doesn’t seem to know I’m pushing the break. I checked both switches on the break pedal and if I did the ohm test right the switches seem to be working. I really think it has something to do with the brake. Is there any terminals I can check for the brakes? I’m lost

 

[I need coffee]

Ok. I changed the ipdm. Still won’t start. I rechecked all the terminals we talked about again but this time with a DVOM. All the terminals have voltage as normal except 80. Still nothing there. I checked on the brake switch. It is giving me the message to press brake, when I push the brake it doesn’t go off. I also cycled the push button like jbarnett250 said and it doesn’t seem to know I’m pushing the break. I checked both switches on the break pedal and if I did the ohm test right the switches seem to be working. I really think it has something to do with the brake. Is there any terminals I can check for the brakes? I’m lost

The brake lights come on, correct? When you push the brake pedal, battery voltage flows through the switch and then back to the fuse box under the dashboard where it branches out in at least three directions--to the tail lights, to the BCM (Terminal #118), and ABS Control Module (Terminal #16). If the brake lights come on then the switch works and voltage is flowing through it although I suppose there's a possibility of a wiring problem in the fuse box or further downstream preventing the voltage from reaching the BCM. Pushing the brake pedal doesn't make that notification on the dashboard go away--it turns off when the engine starts.

A few thoughts before moving on: Did you disconnect the battery at any point before installing the new IPDM? This should clear any BCM DTCs that might prevent the engine from cranking. Also, did you confirm the position of all the fuses in the replacement IPDM and that the fuses are still good (i.e. none are blown)? I would also suggest running the IPDM Auto Active Test to at least confirm the IPDM properly operates the components it directly controls that are easily visible.

If all that checks out, try measuring voltage at IPDM Terminal #46 (brown wire) while trying to start the engine (i.e. foot on brake and push-button start) to confirm whether or not the BCM grounds the control side of the starter relay--if it is then I would expect the voltage on Terminal #46 to drop to zero when the circuit is closed.

Sorry you're having to go through all this. This has turned out to be a tough one.

 

[jbarnett250]

When I read through the starting system debug flowchart it sends you to the security control system chapter to debug the lack of S terminal voltage. Within the security control system chapter I get stuck on the power supply position table. The way I read the table below is that if you have your foot on the brake and the car knows you have your foot on the brake, it will NEVER go to the OFF/lock position if the engine doesn't start. It will always try to go from whatever position it's in to the start position. If either you don't have your foot on the brake or the car incorrectly thinks you don't have your foot on the brake, it will cycle as described below to the off/lock position. This is how you know if the car can detect your foot on the brake pedal. If you hold your foot on the brake and keep it there and push the button repeatedly and the car ever goes to the off state (no dash lights), the car doesn't know you have your foot on the brake.

I recall seeing this behavior now when I was debugging my bad starter. I was fooling around with the brake switches because I read it on the internet and when you disconnect one of them (or both I forget), the car will not shut off because it thinks you have your foot on the brake pedal and you're stuck in that one row of the table. Using that table below, it should be possible to determine if the car knows you have the brake interlock satisfied. If the brake interlock is satisfied, the car should repeatedly try to crank and fail and remain in one of the on states (acc or on). If it isn't satisfied, it will cycle around with multiple presses to the off position. How your debug goes depends on which of these paths you end up on. If the brake interlock is not satisfied then you have to figure out why. Sounds like you've measured the switches. There's also continuity to the BCM. That's also covered in the security control system chapter. If the brake interlock is satisfied and the car is trying to crank but the signal is not making its way to the S terminal, then you go down that path.

But I still think the first thing to do is spend 1 minute going through that table and seeing if the car cycles through the power positions with your foot on and off brake to be certain you're going down the right path. No parts, no disassembly, no measurements even. Just some basic observations. Good luck. Either path might be tough if the easy fixes are already eliminated (brake switch, starter relay, etc.).

 

[Scottrodds]

The voltage on terminal 46 does drop to zero. I did the IPDM test and everything worked as it should. I also did the push button start according to the table above. Everything seemed right. When you push the brake and hit the button it does everything but start( it makes a very faint clicking noise briefly). And it stays in the “ON” position as long as you will let it until you hit the button again.

 

[I need coffee]

The voltage on terminal 46 does drop to zero. I did the IPDM test and everything worked as it should. I also did the push button start according to the table above. Everything seemed right. When you push the brake and hit the button it does everything but start( it makes a very faint clicking noise briefly). And it stays in the “ON” position as long as you will let it until you hit the button again.

I think this is actually good news. If the voltage on Terminal #46 is being pulled down to zero then the BCM is grounding the circuit and it would only do that if the necessary engine start conditions are met.

My next move would be to see if the starter control relay is getting voltage from the starter relay. There are two black relays visible on the top of the IPDM and the one on the driver side of the car is the starter control relay. See if you can remove the relay to do some more voltage testing. You'll need two thin flat-head screwdrivers on each side of the relay to apply upward pressure and a lot of patience since you don't want to damage the relay cover trying to get it out. It will come out though, just take your time and be careful.

Once the relay is out, use the picture below to test the relay sockets:

• Control-Side Power from TCM to IPDM Terminal #72: Battery voltage with ignition ON only.
• Power from Starter Relay: Battery voltage with cranking engine (ignition ON, foot on brake, push start button)
• Continuity Test Power to Terminal #80: With ignition OFF, unplug connector F12 and test continuity from relay socket to IPDM Terminal #80.

 

[jbarnett250]

Oh man I thought the relays were soldered to the board and not accessible to measure. I thought it was odd that they'd be exposed like that but not be removable. But they're so recessed it looks like they might not be removable... not easily anyway. If we can measure the signals upstream of pin 80 all the way back to the battery, it's possible to confirm if the car is trying to crank or not and find out where the signal gets lost on the way to pin 80. Super unlucky that both IPDMs would have a problem though.

Based on the description of the clicking you heard, that sounds like the noises my car made when trying to crank when I had a bad starter. The car is probably trying to crank so you just have the measure the relay control pins and contact voltages that coffee pointed out and you should find it. You're almost there...

 

[Scottrodds]

I’ve got voltage on power from tcu 72. No voltage on power from starter relay. I didn’t know where to hook the leads to do the continuity test?

 

[I need coffee]

I’ve got voltage on power from tcu 72. No voltage on power from starter relay.

Check for battery voltage at IPDM Terminal #36 (green wire) with ignition OFF. If there's no battery voltage at that terminal then check Fuse I (40 amps) in the fusible link block next to the IPDM and make sure it's good.

I didn’t know where to hook the leads to do the continuity test?

Just touch one lead to that pin in the relay socket and the other on Terminal #80. This is really just to confirm there's no break in the circuit between the starter control relay and Terminal #80--I doubt there is, but always good to check.

 

[Scottrodds]

There is continuity on 80 and there is voltage on 36.

 

[I need coffee]

Just to confirm where we are right now:

• Terminal #46 (Starter Relay Solenoid - brown wire) has battery voltage with ignition on, but drops to zero voltage when trying to start the engine (foot on brake pedal w/ push start button).
• The starter control relay socket does NOT have battery voltage at the pin that runs to the starter relay (...and you made sure the probe is touching the metal pin in the relay socket)?

In a previous post after installing the replacement IPDM, you said the engine wouldn't start, but you heard a faint "clicking" noise. I suspected that was the starter relay. Temporarily reinsert the starter control relay (you can wrap a string around it to make it easier to remove again) and try the engine start again and listen to see if you can locate the clicking noise (preferably with a mechanic's stethoscope). The starter relay is literally in between the cooling fan #3 and starter control relays except it's under the plastic cover. I want to verify if that's what's clicking.

 

[Scottrodds]

Ok so I double checked the 46 brown wire and it is NOT losing voltage when button is hit. The starter control relay socket does have 1.5 volts at pin. I can’t say for certain but there is definitely a click near that starter relay area

 

[I need coffee]

Ok so I double checked the 46 brown wire and it is NOT losing voltage when button is hit. The starter control relay socket does have 1.5 volts at pin. I can’t say for certain but there is definitely a click near that starter relay area

Damn. So, it looks like the BCM is not grounding the starter relay circuit after all. I'm not sure what that 1.5 volts on the starter control power socket is...that circuit does also connect to the IPDM, which I suspect is a sensing wire so maybe it's residual voltage from a transistor in there or something. There is no official testing procedure for the starter control relay outside of tests that can be run from the factory scan tool (CONSULT-III) since Nissan doesn't consider that relay serviceable even though you can physically remove it.

I think you're going to have to go right to the BCM and confirm that voltage from the starter relay is present and you can also test for voltage coming from the stop lamp switch while you're there. Unfortunately, you'll have to remove the instrument cluster to get to the BCM. You can find the procedures in the "Meter, Warning Lamp, and Indicator" file and "Instrument Panel" file (for the cluster lid) of the service manual: https://www.nicoclub.com/nissan-service-manuals

Voltages at the BCM should be as follows with ignition switch on unless otherwise noted:

Terminal #47 (Ignition Relay Control; Blue Wire): Battery voltage w/ ignition in OFF or ACC; 0.0 volts with ignition in ON.​

​

Terminal #52 (Starter Relay Control; Red Wire) : Battery voltage in P/N; 0.3 volts in any other gear; 0.0 volts with ignition OFF.​

​

Terminal #118 (Stop Lamp Switch; Blue Wire) : 0.0 volts with foot OFF brake pedal; Battery voltage with brake pedal DEPRESSED.​

​

Terminal #140 (Start Relay Power from TCM; Green Wire): Battery voltage in P/N; 0.0 volts in any other gear.​

For Terminal #52, also measure voltage while trying to start the engine (foot on brake pedal and push-button start) to see if voltage gets pulled down to 0 volts indicating the BCM is grounding the control side of the starter relay.

This is a time where it's really useful to have a scan tool that can read body codes. I'm pretty sure there's some fault codes logged in the BCM that might be helpful in troubleshooting.

 

[I need coffee]

BTW, your first post jumped right into diagnostics and it may be helpful to know if there was anything going on with the car prior to the no-start. Were there any weird electrical issues or anything not working before this? Or, was everything fine and then the engine just suddenly stopped starting? Any prior problems with rodents?

If you can think of anything that was going on with the car before all this then post it, even if it doesn't seem relevant.

 

[Scottrodds]

It’s my daughter’s car. I asked her the same thing and she said she didn’t notice anything. She said it may have felt like the rpm’s were higher when she drove it. But I think that is her imagination lol. Think it would be a good idea to haul it to Orieleys and get them to run the codes? Thanks for all the help so far.

 

[jbarnett250]

Something doesn't add up in the descriptions of the IPDM terminals. Pin 72 gets set to battery voltage when the TCM detects the trans in P or N. Pin 46 should go low when start condition is satisfied but the description in PCS is the opposite and it doesn't even mention the brake but that requirement is described in the SEC chapter. This has got to be a typo. If they put battery voltage on both sides of the relay coil, it wouldn't close and pass battery voltage to the starter control relay.

From the power control chapter (PCS):
IPDM terminal descriptions:

I'm curious why we didn't measure the coil drive signal on the starter relay control relay (the one pin not labeled in coffee's diagram). If you see that go low after pushing start, it would confirm that the BCM is sending the starter request via CAN to the IPDM and the CPU in the IPDM is able to receive the request and command the starter control relay. It's right there and we measured all the other pins in that relay. Why not make one more measurement to learn those extra pieces of info? It seems like we're assuming all that is happening and the source of the problem is no voltage from the starter relay. But now that it looks like 46 is not going low, maybe the BCM isn't pulling it down or sending the start request either. It's easier to measure at the starter control relay coil than accessing the BCM to find out if the BCM is actually sending the start request. Based on the power mode observation that the car stays on no matter how many times you press the start button with foot on brake, this confirms the start conditions are met. There's no other way it stays on. So the BCM should be pulling 46 low and sending the start request via CAN but 46 doesn't go low. Is it not sending the start request either? Measuring that relay coil drive could confirm if the request is being sent/received and acted on by the CPU. If the IPDM is driving the starter control relay coil low, then that would confirm 100% that the problem is that the BCM is not able to pull pin 46 low (as opposed to it's not trying to pull it low).

How many bad BCMs or wiring harnesses have the long timers here seen?

 

[Scottrodds]

Ok. Which pin is it and I’ll measure it.

 

[I need coffee]

Something doesn't add up in the descriptions of the IPDM terminals. Pin 72 gets set to battery voltage when the TCM detects the trans in P or N. Pin 46 should go low when start condition is satisfied but the description in PCS is the opposite and it doesn't even mention the brake but that requirement is described in the SEC chapter. This has got to be a typo. If they put battery voltage on both sides of the relay coil, it wouldn't close and pass battery voltage to the starter control relay.

The description in the FSM is correct. With just the ignition on there will be battery voltage measured at either end of the relay solenoid since the circuit is not live.

I'm curious why we didn't measure the coil drive signal on the starter relay control relay (the one pin not labeled in coffee's diagram).

If the OP found battery voltage at the starter control relay power feed then that would have been the next step although you make a good point that this could have been tested at the same time. I've been trying to break things down into small chunks so it's not too much at once. I'll add that to the relay diagram and repost it.

How many bad BCMs or wiring harnesses have the long timers here seen?

Probably a handful of suspected bad BCMs, but I don't recall if any were confirmed. Unfortunately, may people just don't come back to report what the final fix was.

 

[I need coffee]

Ok. Which pin is it and I’ll measure it.

He means the pin in the starter control relay socket that wasn't labeled in the previous picture I posted. I'm re-posting below with it labeled. That pin is the ground-side control of the starter control relay solenoid and it's operated directly by the IPDM. Probe that terminal in the relay socket with a test light connected to battery positive and see if it lights up while attempting to start the engine (foot on brake pedal and push start button). If it does then that means the IPDM is receiving the start signal and trying to ground the solenoid to send power to the starter.

But, since you are not seeing voltage drop on IPDM Terminal #46 then the BCM is apparently not grounding the starter relay solenoid to allow power to flow through to the starter control relay. So, you've probably noticed that we're headed in the direction of some problem with the BCM or wire going from the IPDM Terminal #46 to the BCM (...hopefully the latter). In fact, unplug IPDM connector E11 and test Terminal #46 (brown wire) at the harness connector and see if you measure any voltage with ignition ON and the transmission in some other gear besides P/N (e.g. put it in D).

 

[I need coffee]

@Scottrodds,
If you still have the original IPDM that was taken out of the car, take a resistance measurement with your DVOM between Terminals #46 and #72. I got approx. 322 Ohms on my "spare" IPDM on the bench. I just want to see if what you measure is consistent with what you found when checking for battery voltage from the TCM on Terminal #46 (i.e. you found nothing with the IPDM connector plugged in and unplugged).

 

[Scottrodds]

Ok. So I haven’t done anymore testing. I took it to two different part stores and they tried to read the codes. But at each different store neither could get their scanner to connect?