Question about Jeep Grand Cherokee

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Pin 30 on 02 sensor relay on 2001 4.0L jeep should it have 12v at all times

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Great question and great digging , you have bad 02.
im sad because you didnt post the symptoms or evidence.
real said, so i can get on the same page...
so you found out it has a relay... but which one?
the ASRD relay or the down stream relays (I guess at down)

it is a grand cherokee right and has 4l. good.
wow 16 pages on 02 alone, just schematics.
left bank, or right bank, always post sensor code like this
B1S2, B2S1... see? so i dont have to read all 16 pages.
ill take the wild assumption B1S2. the most important one.
the down stream. relay ,is just a reg. common, SPST relay.
30 and 86 are jumped, (connected) and are 12v key one
or the ASRD is malfing (not saying it is bad) or the fuse is blown
you did check all fuses first , right? with any ohm meter !!!
fuse 16 is pin 30
the output of relay is 87
the control line (coil) is 86, the PCM controls this line using
COMPLEX logic.
so bad to CONTEXT
why are you fiddling down stream ?
got P040x errors, got scan errors for CAT is weak?......
these sensors only test the cat for early or late death
why be here, Smog man? context answer this, or were mis directed
by internet bunny's ?????
this is a great post, one of the few that tell what car. what engine in car.very rare here, kudos.
but no context.
Smog man
car runs bad need help
CEL glows , no scan tool?

Posted on Dec 31, 2013


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I have a 97 jeep grand cherokee that wont crank i have changed everything under the hood and still nothing what can i do to get it back running

fixing car guessing is very very expensive.
why do that, a $10 voltmeter from walfart and bam cause .
a harmless tool. lets humans see electrons, (voltage potential or drop) just like a water pressure gauge, does.
zero pressure, no flow, dead.
its a 97 grand so my guess its and automatic trans.
no engine stated, so i cant guess the matching box, so...
we do this, GENERIC.

here is a no crank page (called a class 1 failure, dead starter)
you cant drive car with a silent engine, DOA.

first off , there can be 2 ways for a car with a good battery and starter not to crank.
what are they, the park neutral switch dead, or the immoblizer.
skim.skis. angry.

if you had checked the starter relay first.
with a meter , you'd already have cut the problem in 1/2
(saving you the cost of the other half not bad, in 5min work)
using a VOLTMETER.
so car will not crank jumper cable started, (all reg. folks do this first or call AAA Tow and he does it for you)
ok he fails. starter is dead. still.

then this car is ZJ jeep the FSM book is free, posted here
300 times now. not again. ever. search.

here we go, with path checks
PDC fuse 8 good. 12v both sides, ok good.
now the Start relay there, 4 pins
pin C6 hot all time. 12v. white wire (WT)
pin c7 LG-bk wire goes hot cranked, if not forget starter bad.!!!
if the relay clicks and c9 is dead, the relay is bad. (easy no?)
if relay fails to click bingo , (P/N dead)
pin C8 YL-RD wire is hot cranked. if is good. if not? then key switch bad. (dead start pin)
pin C8 must be 0v cranked, or the Park/Neutr, switch is dead.
cranking voltage can be 10 to 12v. ok. (lower in Alaska)

easy no?
the skim immobilizer does not cut cranking , only fuel.
so dont replace that too.

the real deal.
my photo are large and clear but fixya wrecks them. all.


Jul 01, 2016 | 1997 Jeep Grand Cherokee

1 Answer

No power to coil with ignition on. Power at pin 30 all the time and pin 86 with ign on. negative at pin 87. 12v at pin 85.turn key on power at coil for 2 sec. Power at cavity 3 at comp. Fuel pump ok. Code...

Mike, I don't know what you are working on, Chrysler? Chevy? Chrysler and Jeep have an Automatic Shutdown Relay for power to the coil. But the only thing I know that gets a 2 second signal with key in on, is the fuel pump relay. The pcm sends a 2 second signal to pin 85 or 86 of the FP relay with key on to prime the fuel system. Do you need a wiring diagram?

Mar 16, 2015 | Cars & Trucks

1 Answer

Why won't my horn work on my 1991 jeep cherokee laredo?

the horn is simple , a horn a relay and switch, and fuse 15?.

but is complex by other factors.

1: the clock spring . no air bags in 1991, so very easy.

there are 2 ways to diagnose any horn..

1: hot wire it, does it now honk? if yes, hot wire the relay does it honk now?

2: or use any voltmeter ever made and find out why.

#2 is the save way.

id hot wire the horn and make sure that 1991 ground bolt

mount is really still at ground potential. id bet that bolt has

long sense rusted, and is useless, like most are by now.

the fuse and relay are both in the PDC

the PDC means, engine bay fuse box in gringo. (non jargon)

here is 93 for free.

see horn page one and the 2 tests.

or see the schematic.

at there, see the fuse box see fuse 15 (PDC 15?)

same chapter, see PDF page 90 (sheet33)

as you can see if the fuse is good.

12vdc arrives at the Horn relay on 2 pins.

if the horn switch works the relay ENERGIZES (closes)

and 12vdc arrives at the horn, and it honks

if while honking, the horn casing is 12vdc,

then means the horn is no longer grounded, a common happenstance.

if the relay dont energize check the horn ring contacts or connectors to it for continuity.

the relay can be tested, in the car.

like this.


pin 2 and 5 are 12v

pin 1 = 0 volts

pin 4 is 12v, if 0v the relay is bad.

easy huh., ?

May 14, 2014 | 1991 Jeep Cherokee Briarwood

1 Answer

Right side parking lights

usa car, not Renegade or export car. nor DRL lamps.

fuse, can look good but be bad.
use any ohm meter, to make sure they are good. 0 ohms good.
the car can have park-tail relay. yes, it does have a park relay
that feeds 2 fuses (#7&9) then all lamps left and right.
the BCM controls the relay. body brain.

check voltage at all 4 pins of park relay, and bingo know who is messing up,?
pins 86/87 hot 12v all the time( battery)
87a = ground 0v all times.
30 is relay output, 12v park on.
85 pin is relay coil control. 0v park, 12v not park.
if you have 0v on 85 , in park the BCM is working

there is start.
if a fuse is blown to the BCM, it will mess up

Jan 06, 2014 | 2004 Jeep Liberty

1 Answer

I have a 1997 jeep grand cherokee laredo and my headlights stay on after shutting my jeep off,

head lights are designed to work , with no key near car.
its a safety feature. lights always must work. (all answers USA)
this car has many options and funny business with lamps.
like automatic HL sensors.
HL sw. auto, off , park low, see auto, bingo. that option.
on this car the HL switch is ONLY a digital input to the BCM.
body puter.
option 2, is DRL, daylight running lights, GOT DRL?
if you had a real FSM, you'd see all this STUFF.
i will not explain your system. in word, the FSM has 10 schematics on this complex system. (vastly complex to my simple wrangler)
the HL are both grounded
so the system applies 12v power to make them glow.
the 1st fail path is DRL, it can fail and turn them on. (unplug it?)
there is a head light relay that can stick on, or is commanded to do so.
i start there at the the relay.
im sure your relay is closed (enegized) full time. (wrong)
this is because it is bad (pull it see lamps go off , proof)
if pin C10-12 (85 coil) is low , not 12v, on the relay , it is being commanded to be enegized.
there are 3 things that can do that.
1: BCM, body computer sees you switch HL on.
2: automatic HL (dark outside) tune them on. (not key off)
3: DRL (not key off)
so if Auto HL module fails, it can in fact energize the HL relay.
unplug it.
if the DRL messes up, it too can energize the HL relay.
so unplug them all 1 by.
Auto HL module
DRL module
last BCM connector C2 pin 12, pulled, cuts the BCM.

any can fail.
oddly the DRL can mess up the low beams and high..

Nov 22, 2013 | Jeep Wrangler Cars & Trucks

1 Answer

How do I check my main relay? 87 Honda accord lxi

check, ?
ok all relays
the relay is just a coil (mag) and a switch.
many relays have just 4 pins.
most main relays have 2 pins at 12v. one on the coil and one on the common contactor pin (input)
the ECU/PCM grounds the other coil pin, the mag field inside builds and the contactor closes. and the contactor ouput pin
goes to 12v and the ECU then powers up.

how to check it, is easy, use a voltmeter, (never lies , like other ways)
any DMM , even that cheap one at walfart works great.
set the dial to 20vdc.
conn, black lead to car body, metal.
conn red lead to the 4 pins, 1 at at time and key on. (no start)
if the 2 pins do not have 12v(input pins) the fuse is blown or some dork cut the wires to install some , accessory.
now see the ECU ground the othe coil pin, 0volts,
the relay is now energized, (coil must not read infinity removed)
now check the output pin on said relay, if 0v , the relay is bad.
if 12v, on this pin, well , the relay is 100% OK.

to work on cars, you must learn electrics first, then how relays work. there are millions of web pages on this subject,

ok , i went to (so can you)
and that car has 7 pin, MAIN relay.
black yell and blue black pins are 12v keyon.
yellow wire is fuel pump (early cars have 2 relays in one)
black is ground, if open , all is dead ! must be 0v
fuel pump enable line is green-black (ecu commanded)
0v when active, most cars take cranking to go active.
the blue-red wire from crank fuse. sends 12v to pump relay coil
for crank pump action.
and last but not least is the yell-black wire, this wire runs the ECU
and all injectors. this is 12v key on. if not check all coil pins on main.
i answered in the generic and exact.

old post. but lots of old handa's still ,

all this is on or at mitchels.

Sep 30, 2013 | 1987 Honda Accord

1 Answer

2005 Jeep Grand Cherokee font wiper problems. wipers will not park all of the time. when you start Jeep or shut off vehicle, wipers will cycle once. switch is in the off position. dealer replaced wiper...

both blades fail to park.?
are the arms installed correctly?
so the wipers run , when you key on. ? is that it
tell me when exactly they move, and you didnt commend it.
here is how i do this, i log in to
and see its a complex set of 5 parts, in the wiper schematic
2 relays (on/off and hi./low) and the wiper motor and the switch
and the controller.
so i take my handy voltmeter ($10 at walfart) and measure
pin 30 of the wiper relay on/off.
if it reads 12vdc (keyon, or off, with wipers off) this is a bad reading
if it reads 0v, , its good. easy huh
but what if the relay 30 pin read 12v
what would i do, id see if its being told to turn on.
id pull it out, is the wiper dead now. (yes, might be bad relay)
but id check the voltage across the 85/86 relay coil pins
12v is bad, the IPM is commanding wipers full time. (keyon)
0v is good, and relay is TOAST>

The IPM is the thing that holds the wiper switch.
it too can fail but i bet not.

Aug 28, 2013 | 2004 Jeep Grand Cherokee

1 Answer

My carhas been over heating and i noticed my fan is not working on my ratiator. could it be just a fuse

Could be a fuse or a relay, could be coolant temperature sensor/fan switch. It could also be that the fan motor has failed. If the fuse is good, test the fan and relay by jumping pins 30 and 87a at the rad. fan relay socket. If the fan comes on, replace the relay and retest. You can also check for 12v signal and ground on the other pins when the engine is hot to verify the temp. sensor is operating normally. If no 12v or if there is no ground on the rtelay control pins (NOT 30 and 87a), the sensor is probably bad. If the sensor is good and relay is good, 99.9% chance the fan motor is bad, even if it starts when relay is bypassed. The motor takes more power to start than to keep running, and can disrupt operation of the relay if it is marginal. Also look for corroded contacts, esp. ground wire connections.

Jun 21, 2010 | 2001 Dodge Stratus

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