feat: Create comprehensive ECU power supply diagnostic test plan
- Added symptom reference guide (what to see/not see with key ON) - 7-step diagnostic test plan: 1. Basic power check (dash lights, fuel pump prime) 2. ECM fuse voltage test (both sides - corroded contacts) 3. ECU relay swap test 4. Fuse box inspection (water damage/corrosion) 5. ECU power pin test (verify 12V at connector) 6. ECU ground pin test (<1 ohm) 7. Fusible link test (continuity + voltage) - Test decision tree for troubleshooting flow - Priority order (immediate tests first) - Documentation template for recording results - Based on similar GM Express/Savana cases found online - Answers John's questions: dash lights, check engine light, multiple ECU power points
This commit is contained in:
John Loper II
+300
-14
@@ -416,23 +416,309 @@
|
||||
|
||||
---
|
||||
|
||||
## 📊 Next Steps
|
||||
## 🧪 Comprehensive ECU Power Supply Diagnostic Test Plan
|
||||
|
||||
### IMMEDIATE (Do This Before Buying Another ECU):
|
||||
1. Check ECU fuses with multimeter
|
||||
2. Check ECU relay - try swapping
|
||||
3. Inspect fuse box for water damage
|
||||
4. Check ECU power/ground pins
|
||||
**Purpose:** Systematically prove or disprove each potential power supply issue
|
||||
|
||||
### IF POWER IS GOOD:
|
||||
- Then ECU is actually bad
|
||||
- Buy replacement ECU
|
||||
- eBay ECU should work once power is good
|
||||
---
|
||||
|
||||
### IF POWER IS BAD:
|
||||
- Fix the power issue
|
||||
- eBay ECU might work after fix
|
||||
- **Save $300-500!**
|
||||
## 📋 Symptom Reference Guide
|
||||
|
||||
### What You Should See (Normal Operation with Key ON):
|
||||
- ✅ All dash lights illuminate (battery, oil, check engine, etc.)
|
||||
- ✅ Check engine light STAYS ON (not flashing, not off)
|
||||
- ✅ Fuel pump PRIMES (you hear it run for 2 seconds)
|
||||
- ✅ Gauges sweep and return to normal
|
||||
- ✅ Security light goes OFF (after relearn, if applicable)
|
||||
- ✅ Radio works (if equipped)
|
||||
- ✅ Power windows/locks work
|
||||
|
||||
### What You Should NOT See (Indicates Power Problem):
|
||||
- ❌ No dash lights at all (ECU has NO power)
|
||||
- ❌ Check engine light OFF (ECU not powered)
|
||||
- ❌ Fuel pump doesn't prime (ECU not triggering relay)
|
||||
- ❌ Gauges don't move (ECU not receiving ignition power)
|
||||
- ❌ Security light stays ON or flashes (ECU not communicating)
|
||||
- ❌ Radio doesn't work (ignition power issue)
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 1: Basic Power Check (Key ON Position)
|
||||
|
||||
### Purpose: Determine if ECU is receiving ANY power
|
||||
|
||||
### Procedure:
|
||||
1. Turn key to ON position (don't crank)
|
||||
2. Observe dash lights
|
||||
3. Listen for fuel pump prime (2 second hum)
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Symptom | Interpretation |
|
||||
|---------|----------------|
|
||||
| ✅ All dash lights + fuel pump prime | ECU has basic power - power supply likely OK |
|
||||
| ❌ No dash lights at all | ECU has NO power - major power supply failure |
|
||||
| ❌ No fuel pump prime | ECU not triggering fuel pump relay - ECU not receiving power or not functioning |
|
||||
| ❌ Check engine light OFF | ECU not powered (should be ON with key ON) |
|
||||
|
||||
### Conclusion:
|
||||
- **If NO dash lights/fuel pump:** Major power supply failure (fuse, relay, fusible link)
|
||||
- **If dash lights work but no spark:** ECU has power but not sending trigger - could be ECU or power issue
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 2: ECM/PCM Fuse Voltage Test
|
||||
|
||||
### Purpose: Verify fuse has power on BOTH sides (corroded contacts prevent power flow)
|
||||
|
||||
### Procedure:
|
||||
1. Locate ECM/PCM fuse in under-hood fuse box (20A)
|
||||
2. Set multimeter to DC voltage
|
||||
3. With key ON, measure voltage at BOTH sides of fuse
|
||||
4. Compare readings
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Test Side 1 | Test Side 2 | Interpretation |
|
||||
|-------------|-------------|----------------|
|
||||
| 12V | 12V | ✅ Fuse OK, power flowing through |
|
||||
| 12V | 0V | ❌ CORRODED FUSE CONTACT - power not flowing through |
|
||||
| 0V | 0V | ❌ No power to fuse - upstream issue (relay, fusible link) |
|
||||
| 12V | 9V | ⚠️ HIGH RESISTANCE - corroded contacts, voltage drop |
|
||||
|
||||
### Conclusion:
|
||||
- **If voltage differs:** Fuse contacts corroded - clean or replace fuse
|
||||
- **If no voltage on either side:** Check ECU relay, fusible link
|
||||
|
||||
### Similar Cases Found:
|
||||
- https://gmtnation.com/forums/threads/no-power-to-the-pcm-b-fuse-and-fuel-pump-relay.19314
|
||||
- https://www.2carpros.com/questions/no-power-to-fuel-pump-weird-voltages-at-fuse-box
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 3: ECU Relay Test
|
||||
|
||||
### Purpose: Verify relay is passing power to ECU
|
||||
|
||||
### Procedure:
|
||||
1. Locate ECM/IGNITION relay in under-hood fuse box
|
||||
2. Remove relay
|
||||
3. Check if identical relay exists (horn, A/C, DRL)
|
||||
4. Swap relays - test if van starts
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Test Result | Interpretation |
|
||||
|-------------|----------------|
|
||||
| ✅ Van starts with swapped relay | ❌ Original relay was bad - replace relay |
|
||||
| ❌ Van still doesn't start | Relay OK, problem is elsewhere |
|
||||
|
||||
### Relay Pin Function (Standard 4-pin or 5-pin):
|
||||
- **Pin 85:** Coil ground (ECU controls)
|
||||
- **Pin 86:** Coil power (12V from ignition)
|
||||
- **Pin 30:** Battery power (input)
|
||||
- **Pin 87:** Power output to ECU
|
||||
- **Pin 87a:** Normally closed (if 5-pin relay)
|
||||
|
||||
### Conclusion:
|
||||
- **If relay is bad:** Replace relay (~$15-30)
|
||||
- **If relay is good:** Check fuse box contacts, fusible links
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 4: Fuse Box Inspection
|
||||
|
||||
### Purpose: Check for water damage, corrosion inside fuse box
|
||||
|
||||
### Procedure:
|
||||
1. Remove fuse box cover
|
||||
2. Inspect all fuse terminals with flashlight
|
||||
3. Look for:
|
||||
- Green/white corrosion
|
||||
- Water damage stains
|
||||
- Loose terminals
|
||||
- Burned/melted plastic
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Finding | Interpretation |
|
||||
|---------|----------------|
|
||||
| ✅ Clean terminals, no corrosion | Fuse box OK |
|
||||
| ⚠️ Some corrosion on terminals | Clean with electrical contact cleaner |
|
||||
| ❌ Heavy corrosion/water damage | Fuse box needs replacement |
|
||||
|
||||
### Cleaning Procedure:
|
||||
1. Remove fuse box cover
|
||||
2. Spray electrical contact cleaner on terminals
|
||||
3. Use compressed air to dry
|
||||
4. Reinstall and test
|
||||
|
||||
### Similar Cases Found:
|
||||
- https://www.2carpros.com/questions/no-power-to-fuel-pump-weird-voltages-at-fuse-box (disassembled box, cleaned, started on second attempt)
|
||||
- https://bobistheoilguy.com/forums/threads/chevy-express-wont-start-again.337890 (replaced fuse box due to corrosion)
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 5: ECU Power Pin Test
|
||||
|
||||
### Purpose: Verify ECU connector receives clean 12V power
|
||||
|
||||
### Procedure:
|
||||
1. Remove ECU connector
|
||||
2. With key ON, measure voltage at ECU power pins
|
||||
3. Should be 12V on all power pins
|
||||
4. Measure voltage with load (has someone crank engine)
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Voltage Reading | Interpretation |
|
||||
|-----------------|----------------|
|
||||
| 12V-12.6V | ✅ Clean power - ECU should work |
|
||||
| 10V-11V | ⚠️ Voltage drop - check wiring/fuses |
|
||||
| <10V | ❌ Poor power - ECU won't function correctly |
|
||||
| 0V | ❌ No power - upstream issue |
|
||||
|
||||
### Common ECU Power Pins (GM 5.0L):
|
||||
- **Constant 12V:** Battery power (memory)
|
||||
- **Ignition 12V:** Key ON power
|
||||
- **Ground pins:** Should be 0V to chassis
|
||||
|
||||
### Conclusion:
|
||||
- **If voltage is low:** Check fuse contacts, wiring resistance
|
||||
- **If voltage is good:** ECU should work (if eBay ECU is good)
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 6: ECU Ground Pin Test
|
||||
|
||||
### Purpose: Verify ECU has clean ground connection
|
||||
|
||||
### Procedure:
|
||||
1. Set multimeter to resistance (ohms)
|
||||
2. Connect black lead to chassis ground
|
||||
3. Probe ECU ground pins
|
||||
4. Should read <1 ohm (basically 0 ohms)
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Resistance | Interpretation |
|
||||
|------------|----------------|
|
||||
| 0-1 ohm | ✅ Good ground |
|
||||
| 1-5 ohm | ⚠️ Poor ground - clean ground point |
|
||||
| >5 ohm | ❌ Bad ground - clean or replace ground point |
|
||||
|
||||
### Common Ground Points:
|
||||
- Engine block to chassis
|
||||
- Body ground near ECU
|
||||
- Fuse box ground
|
||||
|
||||
---
|
||||
|
||||
## 🔬 Test 7: Fusible Link Test
|
||||
|
||||
### Purpose: Verify fusible links are intact and not corroded
|
||||
|
||||
### Procedure:
|
||||
1. Locate fusible links near battery
|
||||
2. Visually inspect for melted/damaged links
|
||||
3. Test continuity with multimeter
|
||||
4. Test voltage on both sides
|
||||
|
||||
### Expected Results:
|
||||
|
||||
| Test Result | Interpretation |
|
||||
|-------------|----------------|
|
||||
| ✅ Continuity + 12V both sides | Fusible link OK |
|
||||
| ❌ No continuity | Fusible link blown - replace |
|
||||
| ⚠️ 12V on one side only | Corroded fusible link - replace |
|
||||
|
||||
### Similar Cases Found:
|
||||
- https://www.astrosafari.com/threads/ecmb-no-power.14351 (fusible link may have blown)
|
||||
|
||||
---
|
||||
|
||||
## 📊 Test Decision Tree
|
||||
|
||||
```
|
||||
START: Turn key ON
|
||||
|
||||
├─ Do dash lights illuminate?
|
||||
│ ├─ NO → Major power failure
|
||||
│ │ └─ Test: Check battery, main fusible link, ignition switch
|
||||
│ │
|
||||
│ └─ YES → Continue testing
|
||||
│
|
||||
├─ Does fuel pump prime (2 second hum)?
|
||||
│ ├─ NO → ECU not triggering relay
|
||||
│ │ └─ Test: Check ECM fuse voltage (Test 2), ECU power (Test 5)
|
||||
│ │
|
||||
│ └─ YES → ECU has basic power
|
||||
│ └─ Continue to Test 2 (ECM fuse voltage)
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## 🎯 Test Priority Order
|
||||
|
||||
### IMMEDIATE (Do These First):
|
||||
1. **Test 1: Basic Power Check** - 2 minutes
|
||||
- Turn key ON, observe dash lights and fuel pump prime
|
||||
- **Conclusion:** If NO power at all, stop and check main power
|
||||
|
||||
2. **Test 2: ECM Fuse Voltage** - 5 minutes
|
||||
- Check voltage on BOTH sides of ECM fuse
|
||||
- **Conclusion:** If voltage differs, clean/replace fuse contacts
|
||||
|
||||
3. **Test 3: ECU Relay Test** - 5 minutes
|
||||
- Swap with horn relay
|
||||
- **Conclusion:** If van starts, replace relay
|
||||
|
||||
### IF TESTS 1-3 PASS:
|
||||
4. **Test 4: Fuse Box Inspection** - 10 minutes
|
||||
- Look for water damage/corrosion
|
||||
- **Conclusion:** Clean with electrical contact cleaner if corroded
|
||||
|
||||
5. **Test 5: ECU Power Pin Test** - 10 minutes
|
||||
- Verify 12V at ECU connector
|
||||
- **Conclusion:** If voltage is good, eBay ECU should work
|
||||
|
||||
6. **Test 6: ECU Ground Test** - 5 minutes
|
||||
- Verify clean ground
|
||||
- **Conclusion:** Fix ground if poor
|
||||
|
||||
7. **Test 7: Fusible Link Test** - 10 minutes
|
||||
- Check main fusible links
|
||||
- **Conclusion:** Replace if blown or corroded
|
||||
|
||||
---
|
||||
|
||||
## 📝 Documentation Template
|
||||
|
||||
For each test, record:
|
||||
|
||||
| Test | Date | Result | Notes |
|
||||
|------|------|--------|-------|
|
||||
| Test 1: Basic Power | YYYY-MM-DD | Pass/Fail | Dash lights: Yes/No, Fuel pump: Yes/No |
|
||||
| Test 2: ECM Fuse Voltage | YYYY-MM-DD | Pass/Fail | Side 1: __V, Side 2: __V |
|
||||
| Test 3: ECU Relay | YYYY-MM-DD | Pass/Fail | Swapped relay: Yes/No, Van started: Yes/No |
|
||||
| Test 4: Fuse Box | YYYY-MM-DD | Pass/Fail | Corrosion found: Yes/No, Cleaned: Yes/No |
|
||||
| Test 5: ECU Power | YYYY-MM-DD | Pass/Fail | Voltage: __V at pins |
|
||||
| Test 6: ECU Ground | YYYY-MM-DD | Pass/Fail | Resistance: __ ohms |
|
||||
| Test 7: Fusible Link | YYYY-MM-DD | Pass/Fail | Continuity: Yes/No |
|
||||
|
||||
---
|
||||
|
||||
## 💡 Key Questions to Answer
|
||||
|
||||
1. **Does ECU have power at all?** (Test 1)
|
||||
2. **Is power flowing through the fuse?** (Test 2)
|
||||
3. **Is the relay passing power?** (Test 3)
|
||||
4. **Is the fuse box corroded?** (Test 4)
|
||||
5. **Does ECU connector have clean 12V?** (Test 5)
|
||||
6. **Does ECU have clean ground?** (Test 6)
|
||||
7. **Are fusible links intact?** (Test 7)
|
||||
|
||||
**Answer ALL of these before buying another ECU!**
|
||||
|
||||
---
|
||||
|
||||
|
||||
Reference in New Issue
Block a user