Quick answer
P1550 and P1551 are manufacturer-specific (P1) codes, so the exact meaning depends on your make. In the most widely documented cases (such as Nissan/Infiniti), they’re Battery Current Sensor Circuit codes — P1550 = Range/Performance, P1551 = Low Input — part of the charging / battery-monitoring system, not the throttle. On a few makes (notably Volvo), P1550 instead points to the Electronic Throttle Module (ETM). Always confirm the definition for your specific vehicle.
P1550 and P1551 are P1 (manufacturer-defined) trouble codes, which is exactly why you’ll see conflicting definitions online. This guide sorts out what they actually mean by make, then walks through symptoms, causes, fixes and costs — and where a professional scan tool like the iCarsoft CR MAX or CR Eagle speeds up the job.
1What Do the P1550 & P1551 Codes Mean?
Because the second digit is a “1,” these are manufacturer-specific codes — each carmaker can assign its own meaning. The two interpretations you’ll encounter most often are:
| Interpretation | P1550 | P1551 |
|---|---|---|
| Charging system (e.g. Nissan/Infiniti — the common one) | Battery Current Sensor Circuit Range/Performance | Battery Current Sensor Circuit Low Input |
| Electronic throttle (e.g. Volvo) | Electronic Throttle Module (ETM) fault | Throttle control performance fault |
In the charging-system reading, the battery current sensor (usually clamped on the negative battery cable) monitors current flowing in and out of the battery so the ECM/PCM can manage charging. When its signal goes out of range (P1550) or reads low (P1551), the charging strategy is affected. In the Volvo-style reading, the code instead reflects the electronic throttle’s ability to reach commanded positions — frequently carbon buildup in the throttle module.
2Symptoms of P1550 & P1551
Charging / battery-current-sensor reading (most common):
- Check engine light, often with a battery/charging warning lamp.
- Dim or flickering lights; unstable electronics.
- Hard starting or a weak/under-charged battery.
- Occasional stalling and reduced fuel efficiency.
Electronic-throttle reading (e.g. Volvo):
- Reduced engine power or limp mode.
- Poor acceleration or hesitation.
- Rough idle or stalling.
3Common Causes
- Faulty battery current sensor — the sensor itself reads out of range or low.
- Damaged or corroded wiring/connector at the sensor (often on the negative battery terminal).
- Weak or failing battery, which skews the current readings.
- Charging-system fault (alternator/regulator) that the sensor reports.
- Electronic throttle module issue on makes like Volvo — carbon buildup or a failed ETM/throttle body.
- PCM/ECM fault — rare.
4How Serious Is It? Can You Keep Driving?
Diagnose it sooner rather than later. A battery-current-sensor or charging fault can leave you with a flat battery and a no-start at the worst time, and on throttle-related makes the car may drop into limp mode. You can often drive short-term, but don’t ignore it — confirm the cause for your make and repair it.
5How to Diagnose P1550 & P1551
Accurate diagnosis is easier with a capable scan tool such as the iCarsoft CR MAX or CR Eagle, plus a multimeter:
- Read the codes and record freeze-frame data, and check for companion charging codes.
- Confirm the definition for your make before replacing parts.
- Monitor live charging voltage — alternator output should sit around 13.5–14.8 V with the engine running.
- Inspect the battery current sensor and its wiring/connector for damage or corrosion.
- On Volvo-style throttle cases, use component activation/bi-directional tests on the throttle body.
6Steps to Fix
- Scan the system, record freeze-frame data, and look up your make’s definition for the code.
- Charging reading: inspect the battery current sensor on the negative battery cable and its connector; test the battery and alternator output.
- Replace the battery current sensor (or repair wiring) if it’s faulty; replace a weak battery if confirmed.
- Throttle reading (Volvo): clean or replace the electronic throttle module/body and check the throttle position sensor.
- Clear the codes and verify with a test drive, watching live data.
7P1550 / P1551 Repair Cost
| Repair | Typical cost |
|---|---|
| Battery current sensor + labor | $100–$300 |
| Wiring / connector repair | $80–$250 |
| Battery replacement | $150–$350 |
| Electronic throttle module (clean/replace, Volvo) | $100–$800 |
| Diagnostic (scan + voltage test) | $75–$150 |
These are general estimates — confirm the specific cause for your make before buying parts.
8Prevention & Regular Maintenance
- Keep battery terminals and the current-sensor connector clean and corrosion-free.
- Test the battery and alternator annually.
- On throttle-related makes, clean the throttle body periodically to limit carbon buildup.
- Use a diagnostic scanner for periodic charging-system checks and address warning signs early.
9Which iCarsoft Tool to Use
Both tools read and clear P1550/P1551, stream live data and run the tests these codes need. The CR MAX covers all OBD-II functions with full-system diagnostics and live charging-voltage data — the accessible pick. The CR Eagle adds bi-directional/actuator tests and component relearns, useful for confirming a throttle-module or sensor fault after the repair.
Recommended for P1550 / P1551
iCarsoft CR MAX
Full-system, all-OBD-II diagnostics with live charging-voltage data, freeze frame and one-tap code clearing across nearly every brand — ideal for pinning down a battery-current-sensor or charging fault.
$369.95 · CR Eagle $849.95 for bi-directional tests
Shop CR MAX See the CR Eagle10Related Trouble Codes
11P1550 & P1551 — Frequently Asked Questions
What do P1550 and P1551 actually mean?
They’re manufacturer-specific. Most commonly (e.g. Nissan/Infiniti), P1550 = Battery Current Sensor Circuit Range/Performance and P1551 = Battery Current Sensor Circuit Low Input — part of the charging system. On some makes such as Volvo, P1550 refers to the electronic throttle module. Always confirm the definition for your make.
Can I drive with P1550 or P1551?
Often short-term, but a charging-system fault can leave you with a dead battery and no-start, and a throttle fault can cause limp mode. Diagnose and repair it soon.
Are these throttle codes?
Only on some makes (e.g. Volvo). On most vehicles they’re battery-current-sensor/charging codes, not throttle codes — which is exactly why confirming your make matters before replacing parts.
How much does it cost to fix?
Commonly $100–$300 for the battery current sensor and wiring; more if the battery, alternator or (on Volvo) the throttle module is involved.
How do I reset P1550 / P1551?
Fix the underlying fault first, then clear the code with a scan tool such as the iCarsoft CR MAX or CR Eagle.
12References
- SAE International, J2012 — Diagnostic Trouble Code Definitions (defines the P0/P1 framework; P1 codes are OEM-specific).
- Wikipedia, On-board diagnostics — explains why P1 codes are manufacturer-defined.
