Crank no start

07 Jeep Grand Cherokee Laredo 3.7L engine. Currently getting a crank with no start. Rpms do not move while cranking. I have replaced cam and crankshaft sensor. Spark plugs ignition module and fuel pump. I do have fuel pressure. Checked spark plugs after trying to start it a few times. Spark plugs are dry and does not look like a spark has occurred. Seems injectors and coils are not functioning. Have checked fuses and relays with a test light. I noticed injector and coil fuse both are not lighting up. I checked with key in run position and still not lighting up. Fuses are not blown. Have taken them out and pushed them back in to make sure they are seated properly. Seems something that controls both those fuses is the fault. Not sure if it's a bad ground or pcm. Any suggestions would be appreciated. Also no engine codes

Start with a couple simple direction tests.

First is spark. Pick an easy ignition coil to get to, pull it out of the cylinder head but leave it electrically connected. Use your test light connected to B- and use it to test for spark out of the ignition coil while someone else cranks the engine. Vary the air gap to see how much spark you can get out of the coil, if any.

Second is injection pulse. Check for power by unplugging an injector and carefully probing one pin with the test light connected to B-. Again, have someone else crank the engine. If one pin doesn't light up, try the other. One pin should light brightly during cranking.

Doing these checks while cranking the engine is important. This Jeep uses an ASD relay system, meaning that the coils and injectors only get power once the PCM has seen a valid engine speed signal. Checking for power with the key on will tell you nothing.

If you find one of the injector pins lights up during cranking with the test light connected to B-, switch to B+ and do the same thing. Engine cranking, one pin or the other should pulse faintly.

Knowing if there's spark, injection pulse and power to the injectors will help us put you in the right diagnostic direction.

Hi was busy with obligations so took few a couple days to do the tests you advised. While engine cranking I got no spark to ignition coil. I also got no pulse to the injector.

While engine cranking I got no spark to ignition coil. I also got no pulse to the injector.

So the engine is cranking but it appears the ASD relay might not be powering up as Tyler mentioned. The PCM provides a ground to the ASD relay if it sees an RPM signal.

If you have a scan tool now is a good time to verify the RPM signal in graphing mode while the engine is cranking. You should hit 150+ rpm.

Does the scan tool detect an RPM signal?

If there is a signal we head towards the ASD Relay, if not, we head towards the Crank sensor input.

Ok checked rpm on scan tool while cranking. It showed 0 rpms

What would you suggest I check next? Thanks

No RPM signal means no crank signal at the PCM.

I would be checking for a crank signal next using a scope at Pin 35, Connector C2 (orange) PCM. Should be a 5v square wave. A DVOM will show you an average voltage maybe 2.2v cranking.

Just because the sensor is "new", doesn't mean it's good. You might have a wiring issue.

Have any codes come up during all this?

No codes have come up besides an air intake code because I have the air intake off the throttle body. And intake connector is disconnected. I did have codes under the SRS. B212D...would that be more air bag related?

Also I don't have a scope on hand. Just a test light. Anyway to check crank signal without a scope or is that required before I can do more diagnostics?

You are at least gonna need a DVOM to do the checks.

This video will help you immensely:



Here is the sensor wiring diagram;

Should also mention you can backprobe the 3-wire pigtial at Pin 3 and jumper (with a test lamp) with repeated slight taps to the signal wire pin 1 to see if you produce an rpm on the scan tool. This will certainly verify a bad sensor. But Do this test after confirming the 5v ref, the ground are intact.


Here is it's location;

It shows a constant 5v at the power feed even when cranking. No dropoff in voltage. Also ground stayed at that .009. spiked with cranking then dropped back to .009. I also tried the backprobe of pin 3. With the test light. With positive lead from multimeter I tapped on pin 1. With vehicle cranking and in tried in just the on position. Didn't see any rpms on scan tool

Unplug the sensor and repeat the tapping test to see if there is rpm on scan tool. (Key-ON)

While it is unplugged, what is the voltage on the signal wire? (Key-ON). If it is 5v, tap the signal repeatedly to ground. If it is 0v, tap it up to 5v from the 5v reference wire while observing for rpm.

If this doesn't produce an RPM on the tool, the signal wire might be OPEN. You'll have to do the tap test at the PCM.

Just to clarify. Am I backprobing with the test light or the positive side on multimeter?

I'm getting no rpm. While getting 5v at the #3 pin. I tapped with the test light on the ground wire at #2 pin. No rpms detected on scan tool

I tapped on pin #35 on the 2nd pcm plug. I used the positive side of the multimeter. No rpm signal on the scan tool. Voltage was at 4.5 at pin #35.

Dont short 2 and 3 at the sensor. We either want to short (repeated taps) the signal pin 1 to either the 5v ref pin 3 to pull it up or pull it down by tapping the sensor ground pin 2 while unplugged with key on!

To be clear, do you have 5 v on the signal wire (PIN 1) at the sensor unplugged? Because you stated there is 5v at the PCM C2 Pin 35.

If you do:

At the sensor unplugged, use the test light and repeatedly short pins 1 and 2 to bring down the voltage, do you have RPM?

If you don't there is an open between the Sensor Pigtail and the PCM.

In between these tests you should be cycling the key to re-initiate the PCM. Or clear codes, because unplugging the CKP with the key-on should set a code.

Yes I do have 5v on the signal wire at pin #1. I have not been able to get an rpm signal on the scan tool. I repeatedly tapped with the test light pins 1 and 2 on the connector. Had the positive from multimeter on pin 3. Cleared codes and turned key off and back on. I thought for a split second I saw rpms go to 4 at one point. I couldn't get it show rpms again. So wondering if I didn't see it correctly. Also can hear the relay clicking on and at times the throttle body open up when tapping on pins 1 and 2

Good, that clicking would not happen unless the pcm thought the engine was cranking. Replace the Sensor with an OE one.

Just verify the sensor ground is good, test lamp to B+ and touch pin 2, lamp should light.

And with a volmeter to bat negative while cranking test pin 3, voltage should remain stable.

The signal wire integrity is good because of you trying to pull down the circuit and activating relay ( probably the ASD relay which powers the Coils and Injectors). You could test that theory, do the tap test while seeing if they power up with a test lamp!!!!)

Just wanted to give a follow up. I called the local Chrysler/jeep dealership near me for a crankshaft position sensor. They didn't have it in stock. So I went to advanced auto and bought a car quest brand crankshaft sensor. Installed it just to see what would happen. It intermittently started but stalled out immediately each time it would start. So won't stay running. Before I purchase it online, does that confirm to you to definitely get the OEM sensor?

Start and Stall on a Chrysler is a Security issue!

Key-on, look for the little solid red circle on the instrument cluster (Lower left maybe for that year), after about 2 seconds it should go out.

If it doesn't, the engine will crank and only run for 2 seconds.

Sounds like your crank sensor may be ok for now, but you got some KEY/SKREEM/SECURITY issues.