Ignition switch/ECM question

[AntonyJ1214]

Hello all,

I have a 1997 Blazer with the 4.3 and when I try to start it the motor cranks but wont start. No dash lights come on (CEL, ABS, Battery, or anything) I have read that the ignition switch is the most probable culprit. I swapped the ECM already and still nothing being as I thought that the problem was the ECM. So I also hooked up my OBD2 code reader and it wont talk to the computer. So would the faulty ignition switch cause the ECM not to get power and not be able to talk to the code reader? Thanks in advance!

[InDeepShitNow]

Originally Posted by AntonyJ1214

Hello all,

I have a 1997 Blazer with the 4.3 and when I try to start it the motor cranks but wont start. No dash lights come on (CEL, ABS, Battery, or anything) I have read that the ignition switch is the most probable culprit. I swapped the ECM already and still nothing being as I thought that the problem was the ECM. So I also hooked up my OBD2 code reader and it wont talk to the computer. So would the faulty ignition switch cause the ECM not to get power and not be able to talk to the code reader? Thanks in advance!

I would check relays/fuses first. Test the relays to make sure they're working properly. Don't swap ignitions just to find out that's not the problem either!

[danielsatur]

There's alot of wear + tear on the ingition switch, the switch doe's supply the battery!
Check some fuse's, they are designed to protect your computer, and control modules.

[InDeepShitNow]

Originally Posted by danielsatur

There's alot of wear + tear on the ingition switch, the switch doe's supply the battery!
Check some fuse's, they are designed to protect your computer, and control modules.

Agreed. Even if there is no wear and tear on an ignition switch, there's either A: fusable link somewhere from ignition to ECM or B: An ignition relay that offers the same protection. Just check those before you buy an ignition.

[mike2004tct]

Originally Posted by AntonyJ1214

Hello all,

So would the faulty ignition switch cause the ECM not to get power and not be able to talk to the code reader? Thanks in advance!

Yes, particularly on '97s, where the switch is a well known problem. Search up in the How To section for Ignition Switch replacement. You'll find plenty of threads on it for '97s.


I had a switch go about 5 years ago. 1 year later, had the same symptoms , but that time it was the EEM (computer). So, if you replaced the EEm (ECM), the switch/harness is most likely the cause.

A couple of things to check;
1) under the steering column, look for a heavy gauge pink wire that runs from the key tumbler area, to a terminal block/harness around the kick-panel by the pedals (around the steering column). Wiggle that wire with the key turned tro "on". If the dash lights up, it's the switch/harness ( the problem is bad contacts inside the harness box attached to the key tumbler)

2) I think it's fuse #12, a 20amp fuse. Remove the fuse and Check to see if you have voltage on either side of the fuse blades. If 12V is present on either side, your problem most likely isn't the switch. If 0 volts on either side of the fuse, ignition switch module is bad.

[AntonyJ1214]

is there a relay for the ECM? and if so where is it?

[AntonyJ1214]

Mike2004tct - are you talking about the ECM Batt fuse??

[mike2004tct]

Originally Posted by AntonyJ1214

Mike2004tct - are you talking about the ECM Batt fuse??

Yes, if no power at it, no power to ECM.

[AntonyJ1214]

im drawing a blank on how to run this damn DMM lol Im gonna have to have one of my electricians come over and check it out. I can tear apart an aircraft carrier for a living but this electrical stuff is a killer

[AntonyJ1214]

also does the key need to be in the on posistion when I check that?

[mike2004tct]

Originally Posted by AntonyJ1214

im drawing a blank on how to run this damn DMM lol Im gonna have to have one of my electricians come over and check it out. I can tear apart an aircraft carrier for a living but this electrical stuff is a killer

Set the dial to Volts DC. Probe the fuse blades with the red lead(plugged into Volts-ohms), black lead(plugged into common-gnd) to ground (door hinge pin or something similar)

[AntonyJ1214]

right but ine has a volts button but you have to toggle back and forth from AC to DC..... I get that part but on the bottom it says mV?

[AntonyJ1214]

and also when I put the dial on the V and put it on DC the numbers jump around and what not. Is that normal? I mean before I even touch the leads to anything.

[mike2004tct]

Originally Posted by AntonyJ1214

and also when I put the dial on the V and put it on DC the numbers jump around and what not. Is that normal? I mean before I even touch the leads to anything.

Touch the leads together, and you should get a reading of 0V.
Not unusual to see a volt or 2 pop up when leads are wondering. But it should stabilize. Not familiar with the mV reading you're getting, don't have that on mine. (don't have it handy, I may have a separate selection for mV. What outlet is the red lead plugged into? Is it labeled 1k?

Anyway, 12V = 12000mV

[danielsatur]

Fuses + fuseable links are for protecion.
Relays allow a small signal to trigger a large signal device.
Example:
A electric fuel pump is going to have a switch, fuse, relay, and a fuel regulator.
Usually anything with large amp fuses will have relays.