Do you know if it is ECM/PCM or BCM controlled ?
Circuit Description (ECM/PCM Controlled)
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.
Circuit Description (BCM Controlled)
Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.
Free wiring diagrams here
http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size . Under system click on engine ,then under subsystem click on starting . Click the search button ,then click the blue link .
If you look at the diagram you will see the ignition switch ,when in start it sends B+ voltage to the ECM/PCM or depending on which system or engine to the BCM . When it see's this input it will energize the starter relay located in the under hood fuse box. This happens if the control module in charge see's another input from the PNP- park neutral position sensor and if no anti-theft system problems .
Good luck !
SOURCE: diagram for 2005 magnum\r\fuse blocks
Here's a link to the owners manual free download. Simply put year and model in and it will bring up your manual.
Fuse block information begins on page 307 and ends on page 312
SOURCE: i need a diagram of the underhood fuse block for
Fuse/Relay Location*Fuse Amp Rating* Description
1 60A** PJB 2 30A** BSM 3 20A** Not used (Spare)
4 30A** Rear defrost 5 40A** ABS (pump)
6 60A** Delayed accessory circuit breaker
7 20A** Power point #2 8 — Not used 9 20A** Power point #1
10 30A** ABS module (valves) 11 40A** PTEC
12 50A** Ignition relay/Starter relay
13 40A** Trailer tow battery, Trailer tow turn signals
14 10A* Foglamps 15 15A* Memory (KAPWR)
16 15A* Headlamp switch 17 20A* 4x4 (v-batt 2)
18 20A* 4x4 (v-batt 1) 19 20A** High beam relay
20 30A** Electric brake 21 30A** Front wiper motor
22 20A** Autolamp; Low beam 23 30A** Ignition switch
24 20A* Rear Fog Lamps 25 – Not used
26 15A* Fuel pump 27 20A* Trailer tow lamps
28 20A* Horn relay 29 60A** PJB 30 20A** Rear wiper motor
31 — Not used 32 — Not used 33 30A** Auxiliary blower motor 34 30A** Power seats, Adjustable pedals
35 20A** Rear power point 36 40A** Blower motor
37 15A* A/C clutch relay/Transmission
SOURCE: 2004 chevy trailblazer fuse box diagrams
I have front and rear a/c. The air is blowing in the back but not in the front. Don I have 2 blowers/units. Could this be a fuse?
SOURCE: wiring diagram for 92 chevy blazer
My Wife Lost the keys to her 92 Chevy blazer so i bought a new ignition key and forced the old ignition cylinder out.The new ignition would not turn forward.So I turned the ignition forward and an alarm come on I didnt no it had.I removed the alarm I ties all the same color wires together now im not getting any power.
SOURCE: 2005 chevy trailblazer was jump
This is a fairly common problem on Trailblazers. What happens most often is, when jump started, instead of connecting the jumper cables to the battery, they get connected to the studs on the main fuse box under the hood. When this happens, it blows the megafuse in the fuse box.
The megafuse feeds electrical current to most of the circuits in the rear fuse box. If that megafuse is blown, it will have to be replaced, and this should fix your problem. Here is a picture I found on the 'net of the megafuse:
Hope this helps!!
Underhood Fuse Block
4.2L Engine
Except Saab
Underhood Fuse Block (2002 - 2005 Early Production)
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