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2002 Land Rover Discovsry
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Discussion Starter #1
Ok guys I need some help. I’m at my wits end.

Cruising down the road, as soon as the truck goes above 2000rpm the lights all start flashing and the truck goes into limp mode.

New battery, new crank position sensor, new negative battery terminal. I can’t figure out what is causing it. I’ve even taken the new CPS out and replugged it in to see if it wasn’t seated properly. This only started happening after I changed the CPS so I feel like it must be related but I can’t understand why.

What do you guys think?
 

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I would recheck the negative terminal install if that was the most recent work


But...

However, this is a low voltage fault....so if you have a new battery I would take it to get it's alternator checked asap. Most issues on this are battery being old or a random terminal cable getting loose after a battery install or being unplugged for work.

An alternator crapping the bed would do this as well, given the age on these vehicles...it's def overdue in some cases
 

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Discussion Starter #4
I would recheck the negative terminal install if that was the most recent work


But...

However, this is a low voltage fault....so if you have a new battery I would take it to get it's alternator checked asap. Most issues on this are battery being old or a random terminal cable getting loose after a battery install or being unplugged for work.

An alternator crapping the bed would do this as well, given the age on these vehicles...it's def overdue in some cases
What’s the best way to check if the alternator is going bad?
 

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Personally (results may vary), jiggle the cables to terminals. Start the car, let warm up....disconnect negative terminal. If it dies, then off to AutoZone or wherever you have access to you go.

Now, I've seen where that does not make your engine stop and the alt was still bad.

IMO, it's not a definite test but it def points in the right direction. After all, if you don't know if the alternator is new or when it was replaced then it could be suspect.
 

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G4 Mike
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With it running the voltage across the battery should be 13.5 to 14.5 volts. If it's not take the alternator in for a test.
 

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What’s the best way to check if the alternator is going bad?
Auto parts stores have diagnostic equipment that will test alternator output, both baseline and under load. My ~$50 home battery charger bought years and years ago has a load test feature built into it.
 

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^^^^^^ all of this.

Super approachable and quickly diagnosed

I had this same issue, it was a loose negative and I just scrubbed all grounds I saw.

Easy fix either way, good luck!
 

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Discussion Starter #9
^^^^^^ all of this.

Super approachable and quickly diagnosed

I had this same issue, it was a loose negative and I just scrubbed all grounds I saw.

Easy fix either way, good luck!
Alright gang. Back to the drawing board. Tested the alternator, battery and starter at oreilleys. Everything passed, and it was reading 13.7 volts with the car running.

Anyone have anything else it could be?
 

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very disco
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It might still be... test your voltage at idle further down the line... say, at the TCM. You could have proper output from the batt/alt, but have a bad ground at the TCM or similar.
 

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You need a proper diagnostic tool to scan the autobx ECU to read live rpm input from it. Generic P1884 code is not enough cos it has 8 subcodes, one subcode is for "engine speed invalid" input which can be caused by the CPS signal, if you had trouble with that and changed it with new one the problem can be with it's circuit, bad contacts in the connector are quite common so insist on that path eventually make a continuity test on the circuit if you know to read a diagram
 

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Discussion Starter #13
You need a proper diagnostic tool to scan the autobx ECU to read live rpm input from it. Generic P1884 code is not enough cos it has 8 subcodes, one subcode is for "engine speed invalid" input which can be caused by the CPS signal, if you had trouble with that and changed it with new one the problem can be with it's circuit, bad contacts in the connector are quite common so insist on that path eventually make a continuity test on the circuit if you know to read a diagram
So the CPS could be a dud? How likely is that? It wasn’t the most expensive thing in the world so I wouldn’t mind getting another one, but man was it a bitch of a job.
 

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Read again what i explained... you have to properly diagnose it
 
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Discussion Starter #15
Read again what i explained... you have to properly diagnose it
Welp, I read it again.... aaaaand I bought a $400 iLand from AB. Hopefully that’ll help me to pinpoint what’s wrong. At the very least I’ll be able to bleed the ABS system so that’ll be a plus.

If anyone has any more ideas, or have seen this problem before let me know. I suppose it could be a bad ground INSIDE the connector harness to the CPS sensor plug. But man, that’d be a weird 1 in a million shot.
 

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Discussion Starter #16
Don’t get me wrong, I LOVE this truck, and so does the wife, but man, I’m getting frustrated I can’t get it running reliably. Like I can’t get the beast over 55mph without the M and S lights flashing because it gets over 2000rpm. It doesn’t make any sense.
 

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That's how it behaves if P1884(35) code is present and on your's it seems that it's corroborated with the CPS fault code... you should be albe to read live rpm(engine speed) input from the autobox ECU with that iLand tool i hope. I've seen many cases when the CPS connector or wiring was the problem. When you said CPS you meant crankshaft position sensor not camshaft sensor i suppose.
 
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Discussion Starter #18
That's how it behaves if P1884(35) code is present and on your's it seems that it's corroborated with the CPS fault code... you should be albe to read live rpm(engine speed) input from the autobox ECU with that iLand tool i hope. I've seen many cases when the CPS connector or wiring was the problem. When you said CPS you meant crankshaft position sensor not camshaft sensor i suppose.
Correct, crankshaft position sensor. What am I looking for in terms of engine rpm? What would be normal/abnormal?
 

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First of all read the full fault code from autobox ECU then with stationary vehicle see rpm reading from the engine ECU while keeping the pedal as fix as you can and keep in mind where the needle is at 2000 - 3000 rpm then read rpm from autobox ECU and compare, if it's difference we'll speak again... anyway you should see a nice growing rpm reading as you push the throttle cos if there are fluctuations the problem is with the CPS input for some reason
 
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Discussion Starter #20
First of all read the full fault code from autobox ECU then with stationary vehicle see rpm reading from the engine ECU while keeping the pedal as fix as you can and keep in mind where the needle is at 2000 - 3000 rpm then read rpm from autobox ECU and compare, if it's difference we'll speak again... anyway you should see a nice growing rpm reading as you push the throttle cos if there are fluctuations the problem is with the CPS input for some reason
So I can tell you there definitely are fluctuations, just from reading the RPM gauge. It gets to 2000, then kicks back down to about 1500 about two or three times in quick succession, and then all the lights come on with limp mode.
 
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